diff --git a/DESCRIPTION b/DESCRIPTION
index 3b4b20a5cf..cbe0a368e2 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -39,6 +39,7 @@ Imports:
     isoband,
     lifecycle (> 1.0.1),
     rlang (>= 1.1.0),
+    S7,
     scales (>= 1.4.0),
     stats,
     vctrs (>= 0.6.0),
@@ -93,6 +94,7 @@ Collate:
     'compat-plyr.R'
     'utilities.R'
     'aes.R'
+    'all-classes.R'
     'utilities-checks.R'
     'legend-draw.R'
     'geom-.R'
@@ -175,6 +177,8 @@ Collate:
     'grob-dotstack.R'
     'grob-null.R'
     'grouping.R'
+    'properties.R'
+    'margins.R'
     'theme-elements.R'
     'guide-.R'
     'guide-axis.R'
@@ -199,7 +203,6 @@ Collate:
     'layer-sf.R'
     'layout.R'
     'limits.R'
-    'margins.R'
     'performance.R'
     'plot-build.R'
     'plot-construction.R'
diff --git a/NAMESPACE b/NAMESPACE
index e7e47740d3..f2c0e9e5dd 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -1,31 +1,34 @@
 # Generated by roxygen2: do not edit by hand
 
+S3method("$","ggplot2::element")
+S3method("$","ggplot2::gg")
+S3method("$","ggplot2::theme")
 S3method("$",ggproto)
 S3method("$",ggproto_parent)
-S3method("$",theme)
-S3method("$<-",uneval)
-S3method("+",gg)
+S3method("$<-","ggplot2::element")
+S3method("$<-","ggplot2::gg")
+S3method("$<-","ggplot2::mapping")
+S3method("[","ggplot2::element")
+S3method("[","ggplot2::gg")
+S3method("[","ggplot2::mapping")
 S3method("[",mapped_discrete)
-S3method("[",uneval)
+S3method("[<-","ggplot2::element")
+S3method("[<-","ggplot2::gg")
+S3method("[<-","ggplot2::mapping")
 S3method("[<-",mapped_discrete)
-S3method("[<-",uneval)
+S3method("[[","ggplot2::element")
+S3method("[[","ggplot2::gg")
 S3method("[[",ggproto)
-S3method("[[<-",uneval)
+S3method("[[<-","ggplot2::element")
+S3method("[[<-","ggplot2::gg")
+S3method("[[<-","ggplot2::mapping")
 S3method(.DollarNames,ggproto)
 S3method(as.data.frame,mapped_discrete)
-S3method(as.gtable,ggplot)
-S3method(as.gtable,ggplot_built)
 S3method(as.list,ggproto)
 S3method(autolayer,default)
 S3method(autoplot,default)
 S3method(c,mapped_discrete)
 S3method(drawDetails,zeroGrob)
-S3method(element_grob,element_blank)
-S3method(element_grob,element_line)
-S3method(element_grob,element_point)
-S3method(element_grob,element_polygon)
-S3method(element_grob,element_rect)
-S3method(element_grob,element_text)
 S3method(format,ggproto)
 S3method(format,ggproto_method)
 S3method(fortify,"NULL")
@@ -51,30 +54,7 @@ S3method(fortify,sfg)
 S3method(fortify,summary.glht)
 S3method(fortify,tbl)
 S3method(fortify,tbl_df)
-S3method(get_alt_text,ggplot)
-S3method(get_alt_text,ggplot_built)
-S3method(get_alt_text,gtable)
-S3method(ggplot,"function")
-S3method(ggplot,default)
-S3method(ggplot_add,"NULL")
-S3method(ggplot_add,"function")
-S3method(ggplot_add,Coord)
-S3method(ggplot_add,Facet)
-S3method(ggplot_add,Guides)
-S3method(ggplot_add,Layer)
-S3method(ggplot_add,Scale)
-S3method(ggplot_add,by)
-S3method(ggplot_add,data.frame)
-S3method(ggplot_add,default)
-S3method(ggplot_add,labels)
-S3method(ggplot_add,list)
-S3method(ggplot_add,theme)
-S3method(ggplot_add,uneval)
-S3method(ggplot_build,ggplot)
-S3method(ggplot_build,ggplot_built)
-S3method(ggplot_gtable,ggplot_built)
 S3method(grid.draw,absoluteGrob)
-S3method(grid.draw,ggplot)
 S3method(grobHeight,absoluteGrob)
 S3method(grobHeight,zeroGrob)
 S3method(grobWidth,absoluteGrob)
@@ -95,27 +75,22 @@ S3method(limits,character)
 S3method(limits,factor)
 S3method(limits,numeric)
 S3method(makeContext,dotstackGrob)
-S3method(merge_element,default)
-S3method(merge_element,element)
-S3method(merge_element,element_blank)
-S3method(merge_element,margin)
 S3method(pattern_alpha,GridPattern)
 S3method(pattern_alpha,GridTilingPattern)
 S3method(pattern_alpha,default)
 S3method(pattern_alpha,list)
-S3method(plot,ggplot)
 S3method(predictdf,default)
 S3method(predictdf,glm)
 S3method(predictdf,locfit)
 S3method(predictdf,loess)
+S3method(print,"ggplot2::ggplot")
+S3method(print,"ggplot2::mapping")
+S3method(print,"ggplot2::theme")
 S3method(print,element)
-S3method(print,ggplot)
 S3method(print,ggplot2_bins)
 S3method(print,ggproto)
 S3method(print,ggproto_method)
 S3method(print,rel)
-S3method(print,theme)
-S3method(print,uneval)
 S3method(scale_type,Date)
 S3method(scale_type,POSIXt)
 S3method(scale_type,character)
@@ -129,7 +104,6 @@ S3method(scale_type,logical)
 S3method(scale_type,numeric)
 S3method(scale_type,ordered)
 S3method(scale_type,sfc)
-S3method(summary,ggplot)
 S3method(vec_cast,character.mapped_discrete)
 S3method(vec_cast,double.mapped_discrete)
 S3method(vec_cast,factor.mapped_discrete)
@@ -308,6 +282,11 @@ export(binned_scale)
 export(borders)
 export(calc_element)
 export(check_device)
+export(class_ggplot)
+export(class_ggplot_built)
+export(class_labels)
+export(class_mapping)
+export(class_theme)
 export(combine_vars)
 export(complete_theme)
 export(continuous_scale)
@@ -347,6 +326,7 @@ export(draw_key_vline)
 export(draw_key_vpath)
 export(dup_axis)
 export(el_def)
+export(element)
 export(element_blank)
 export(element_geom)
 export(element_grob)
@@ -766,6 +746,7 @@ export(xlim)
 export(ylab)
 export(ylim)
 export(zeroGrob)
+if (getRversion() < "4.3.0") importFrom("S7", "@")
 import(grid)
 import(gtable)
 import(rlang)
diff --git a/R/aes.R b/R/aes.R
index de3376071d..8641a952cb 100644
--- a/R/aes.R
+++ b/R/aes.R
@@ -46,8 +46,8 @@ NULL
 #' 'AsIs' variables.
 #'
 #' @family aesthetics documentation
-#' @return A list with class `uneval`. Components of the list are either
-#'   quosures or constants.
+#' @return An S7 object representing a list with class `mapping`. Components of
+#'   the list are either quosures or constants.
 #' @export
 #' @examples
 #' aes(x = mpg, y = wt)
@@ -105,13 +105,12 @@ aes <- function(x, y, ...) {
     inject(aes(!!!args))
   })
 
-  aes <- new_aes(args, env = parent.frame())
-  rename_aes(aes)
+  class_mapping(rename_aes(args), env = parent.frame())
 }
 
 #' @export
 #' @rdname is_tests
-is_mapping <- function(x) inherits(x, "uneval")
+is_mapping <- function(x) S7::S7_inherits(x, class_mapping)
 
 # Wrap symbolic objects in quosures but pull out constants out of
 # quosures for backward-compatibility
@@ -130,14 +129,10 @@ new_aesthetic <- function(x, env = globalenv()) {
 
   x
 }
-new_aes <- function(x, env = globalenv()) {
-  check_object(x, is.list, "a {.cls list}")
-  x <- lapply(x, new_aesthetic, env = env)
-  structure(x, class = "uneval")
-}
 
 #' @export
-print.uneval <- function(x, ...) {
+# TODO: should convert to proper S7 method once bug in S7 is resolved
+`print.ggplot2::mapping` <- function(x, ...) {
   cat("Aesthetic mapping: \n")
 
   if (length(x) == 0) {
@@ -152,26 +147,24 @@ print.uneval <- function(x, ...) {
   invisible(x)
 }
 
+# TODO: should convert to proper S7 method once bug in S7 is resolved
 #' @export
-"[.uneval" <- function(x, i, ...) {
-  new_aes(NextMethod())
+"[.ggplot2::mapping" <- function(x, i, ...) {
+  class_mapping(NextMethod())
 }
 
 # If necessary coerce replacements to quosures for compatibility
 #' @export
-"[[<-.uneval" <- function(x, i, value) {
-  new_aes(NextMethod())
+"[[<-.ggplot2::mapping" <- function(x, i, value) {
+  class_mapping(NextMethod())
 }
 #' @export
-"$<-.uneval" <- function(x, i, value) {
-  # Can't use NextMethod() because of a bug in R 3.1
-  x <- unclass(x)
-  x[[i]] <- value
-  new_aes(x)
+"$<-.ggplot2::mapping" <- function(x, i, value) {
+  class_mapping(NextMethod())
 }
 #' @export
-"[<-.uneval" <- function(x, i, value) {
-  new_aes(NextMethod())
+"[<-.ggplot2::mapping" <- function(x, i, value) {
+  class_mapping(NextMethod())
 }
 
 #' Standardise aesthetic names
@@ -212,8 +205,7 @@ substitute_aes <- function(x, fun = standardise_aes_symbols, ...) {
   x <- lapply(x, function(aesthetic) {
     as_quosure(fun(quo_get_expr(aesthetic), ...), env = environment(aesthetic))
   })
-  class(x) <- "uneval"
-  x
+  class_mapping(x)
 }
 # x is a quoted expression from inside aes()
 standardise_aes_symbols <- function(x) {
@@ -311,7 +303,7 @@ aes_ <- function(x, y, ...) {
     }
   }
   mapping <- lapply(mapping, as_quosure_aes)
-  structure(rename_aes(mapping), class = "uneval")
+  class_mapping(rename_aes(mapping))
 }
 
 #' @rdname aes_
@@ -337,7 +329,7 @@ aes_string <- function(x, y, ...) {
     new_aesthetic(x, env = caller_env)
   })
 
-  structure(rename_aes(mapping), class = "uneval")
+  class_mapping(rename_aes(mapping))
 }
 
 #' @export
@@ -358,10 +350,9 @@ aes_all <- function(vars) {
 
   # Quosure the symbols in the empty environment because they can only
   # refer to the data mask
-  structure(
-    lapply(vars, function(x) new_quosure(as.name(x), emptyenv())),
-    class = c("unlabelled_uneval", "uneval")
-  )
+  x <- class_mapping(lapply(vars, function(x) new_quosure(as.name(x), emptyenv())))
+  class(x) <- union("unlabelled", class(x))
+  x
 }
 
 #' Automatic aesthetic mapping
diff --git a/R/all-classes.R b/R/all-classes.R
new file mode 100644
index 0000000000..586988d665
--- /dev/null
+++ b/R/all-classes.R
@@ -0,0 +1,188 @@
+# S3 classes --------------------------------------------------------------
+
+# Meta classes:
+# TODO: These should be replaced once R 4.3.0 is the minimum version as `+`
+# dispatch should work as intended.
+class_gg    <- S7::new_class("gg", abstract = TRUE)
+class_S3_gg <- S7::new_S3_class("gg")
+
+# Proper S3 classes we need awareness for
+class_ggproto <- S7::new_S3_class("ggproto")
+class_gtable  <- S7::new_S3_class("gtable")
+
+# The important ggproto classes that we treat as S3 classes in S7 even though
+# they are their own thing.
+class_scale  <- S7::new_S3_class("Scale")
+class_guides <- S7::new_S3_class("Guides")
+class_coord  <- S7::new_S3_class("Coord")
+class_facet  <- S7::new_S3_class("Facet")
+class_layer  <- S7::new_S3_class("Layer")
+class_layout <- S7::new_S3_class("Layout")
+class_scales_list <- S7::new_S3_class("ScalesList")
+
+# User facing classes -----------------------------------------------------
+
+#' The theme class
+#'
+#' The theme class holds information on how non-data elements of the plot
+#' should be rendered. The preferred way to construct an object of this class
+#' is through the [`theme()`] function.
+#'
+#' @param elements A named list containing theme elements.
+#' @param complete A boolean value stating whether a theme is complete.
+#' @param validate A boolean value stating whether a theme should still be
+#'   validated.
+#'
+#' @keywords internal
+#' @export
+class_theme <- S7::new_class(
+  "theme", class_S3_gg,
+  properties = list(
+    complete = S7::class_logical,
+    validate = S7::class_logical
+  ),
+  constructor = function(elements, complete, validate) {
+    S7::new_object(
+      elements,
+      complete = complete,
+      validate = validate
+    )
+  }
+)
+
+#' The labels class
+#'
+#' The labels class holds a list with label information to display as titles
+#' of plot components. The preferred way to construct an object of the labels
+#' class is to use the [`labs()`] function.
+#'
+#' @param labels A named list.
+#'
+#' @keywords internal
+#' @export
+class_labels <- S7::new_class(
+  "labels", parent = class_S3_gg,
+  constructor = function(labels) S7::new_object(labels),
+  validator = function(self) {
+    if (!is.list(self)) {
+      return("labels must be a list.")
+    }
+    if (!is_named2(self)) {
+      return("every label must be named.")
+    }
+    dups <- unique(names(self)[duplicated(names(self))])
+    if (length(dups) > 0) {
+      dups <- oxford_comma(dups, final = "and")
+      return(paste0("labels cannot contain duplicate names (", dups, ")."))
+    }
+    return(NULL)
+  }
+)
+
+#' The mapping class
+#'
+#' The mapping class holds a list of quoted expressions
+#' ([quosures][rlang::topic-quosure]) or constants. An object is typically
+#' constructed using the [`aes()`] function.
+#'
+#' @param x A list of quosures and constants.
+#' @param env An environment for symbols that are not quosures or constants.
+#'
+#' @keywords internal
+#' @export
+class_mapping <- S7::new_class(
+  "mapping", parent = class_S3_gg,
+  constructor = function(x, env = globalenv()) {
+    check_object(x, is.list, "a {.cls list}")
+    x <- lapply(x, new_aesthetic, env = env)
+    S7::new_object(x)
+  }
+)
+
+#' The ggplot class
+#'
+#' The ggplot class collects the needed information to render a plot.
+#' This class can be constructed using the [`ggplot()`] function.
+#'
+#' @param data A property containing any data coerced by [`fortify()`].
+#' @param layers A list of layer instances created by [`layer()`].
+#' @param scales A ScalesList ggproto object.
+#' @param guides A Guides ggproto object created by [`guides()`].
+#' @param mapping A mapping class object created by [`aes()`].
+#' @param theme A theme class object created by [`theme()`].
+#' @param coordinates A Coord ggproto object created by `coord_*()` family of
+#'   functions.
+#' @param facet A Facet ggproto object created by `facet_*()` family of
+#'   functions.
+#' @param layout A Layout ggproto object.
+#' @param labels A labels object created by [`labs()`].
+#' @param plot_env An environment.
+#'
+#' @keywords internal
+#' @export
+class_ggplot <- S7::new_class(
+  name = "ggplot", parent = class_gg,
+  properties = list(
+    data    = S7::class_any,
+    layers  = S7::class_list,
+    scales  = class_scales_list,
+    guides  = class_guides,
+    mapping = class_mapping,
+    theme   = class_theme,
+    coordinates = class_coord,
+    facet   = class_facet,
+    layout  = class_layout,
+    labels  = class_labels,
+    plot_env = S7::class_environment
+  ),
+  constructor = function(data = waiver(), layers = list(), scales = NULL,
+                         guides = NULL, mapping = aes(), theme = NULL,
+                         coordinates = coord_cartesian(default = TRUE),
+                         facet = facet_null(), layout = NULL,
+                         labels = labs(), plot_env = parent.frame()) {
+    S7::new_object(
+      S7::S7_object(),
+      data = data, layers = layers,
+      scales = scales %||% scales_list(),
+      guides = guides %||% guides_list(),
+      mapping = mapping, theme = theme %||% theme(),
+      coordinates = coordinates, facet = facet,
+      layout = layout %||% ggproto(NULL, Layout),
+      labels = labels, plot_env = plot_env
+    )
+  }
+)
+
+#' The ggplot built class
+#'
+#' The ggplot built class is an intermediate class and represents a processed
+#' ggplot object ready for rendering. It is constructed by calling
+#' [`ggplot_build()`] on a [ggplot][class_ggplot] object and is not meant to be
+#' instantiated directly. The class can be rendered to a gtable object by
+#' calling the [`ggplot_gtable()`] function on a ggplot built class object.
+#'
+#' @param data A list of plain data frames; one for each layer.
+#' @param layout A Layout ggproto object.
+#' @param plot A completed ggplot class object.
+#'
+#' @keywords internal
+#' @export
+class_ggplot_built <- S7::new_class(
+  "ggplot_built",
+  properties = list(
+    data   = S7::class_list,
+    layout = class_layout,
+    plot   = class_ggplot
+  ),
+  constructor = function(data = NULL, layout = NULL, plot = NULL) {
+    if (is.null(data) || is.null(layout) || is.null(plot)) {
+      cli::cli_abort(
+        "The {.cls ggplot_built} class should be constructed by {.fn ggplot_build}."
+      )
+    }
+    S7::new_object(
+      S7::S7_object(),
+      data = data, layout = layout, plot = plot
+    )
+  }
+)
diff --git a/R/backports.R b/R/backports.R
index 7ccedc4296..53ab2a6f7e 100644
--- a/R/backports.R
+++ b/R/backports.R
@@ -15,6 +15,10 @@ if (getRversion() < "3.3") {
   backport_unit_methods <- function() {}
 }
 
+# enable usage of <S7_object>@name in package code
+#' @rawNamespace if (getRversion() < "4.3.0") importFrom("S7", "@")
+NULL
+
 on_load(backport_unit_methods())
 
 unitType <- function(x) {
diff --git a/R/bench.R b/R/bench.R
index 4d679b8e31..81835836ac 100644
--- a/R/bench.R
+++ b/R/bench.R
@@ -15,7 +15,7 @@
 benchplot <- function(x) {
   x <- enquo(x)
   construct <- system.time(x <- eval_tidy(x))
-  check_inherits(x, "ggplot")
+  check_inherits(x, "ggplot2::ggplot")
 
   build <- system.time(data <- ggplot_build(x))
   render <- system.time(grob <- ggplot_gtable(data))
diff --git a/R/coord-sf.R b/R/coord-sf.R
index d603d57de7..63e5ed4a26 100644
--- a/R/coord-sf.R
+++ b/R/coord-sf.R
@@ -334,13 +334,13 @@ CoordSf <- ggproto("CoordSf", CoordCartesian,
 
     # we don't draw the graticules if the major panel grid is
     # turned off
-    if (inherits(el, "element_blank")) {
+    if (is_theme_element(el, "blank")) {
       grobs <- list(element_render(theme, "panel.background"))
     } else {
       line_gp <- gg_par(
-        col = el$colour,
-        lwd = el$linewidth,
-        lty = el$linetype
+        col = el@colour,
+        lwd = el@linewidth,
+        lty = el@linetype
       )
       grobs <- c(
         list(element_render(theme, "panel.background")),
diff --git a/R/facet-.R b/R/facet-.R
index 94b75148ee..8200a2921e 100644
--- a/R/facet-.R
+++ b/R/facet-.R
@@ -444,9 +444,9 @@ is.facet <- function(x) {
 #' get_strip_labels(p + facet_grid(year ~ cyl))
 get_strip_labels <- function(plot = get_last_plot()) {
   plot   <- ggplot_build(plot)
-  layout <- plot$layout$layout
-  params <- plot$layout$facet_params
-  plot$plot$facet$format_strip_labels(layout, params)
+  layout <- plot@layout$layout
+  params <- plot@layout$facet_params
+  plot@plot@facet$format_strip_labels(layout, params)
 }
 
 # A "special" value, currently not used but could be used to determine
@@ -538,7 +538,7 @@ check_vars <- function(x) {
   }
   # Native pipe have higher precedence than + so any type of gg object can be
   # expected here, not just ggplot
-  if (inherits(x, "gg")) {
+  if (S7::S7_inherits(x, class_gg)) {
     cli::cli_abort(c(
       "Please use {.fn vars} to supply facet variables.",
       "i" = "Did you use {.code %>%} or {.code |>} instead of {.code +}?"
diff --git a/R/facet-grid-.R b/R/facet-grid-.R
index 86bbad2b04..c0b1d7795f 100644
--- a/R/facet-grid-.R
+++ b/R/facet-grid-.R
@@ -206,7 +206,7 @@ grid_as_facets_list <- function(rows, cols) {
       msg <- "{.arg rows} must be {.code NULL} or a {.fn vars} list if {.arg cols} is a {.fn vars} list."
       # Native pipe have higher precedence than + so any type of gg object can be
       # expected here, not just ggplot
-      if (inherits(rows, "gg")) {
+      if (S7::S7_inherits(rows, class_gg)) {
         msg <- c(
           msg,
           "i" = "Did you use {.code %>%} or {.code |>} instead of {.code +}?"
diff --git a/R/geom-.R b/R/geom-.R
index e2d8806b35..94a829f4a8 100644
--- a/R/geom-.R
+++ b/R/geom-.R
@@ -245,7 +245,7 @@ eval_from_theme <- function(aesthetics, theme, class = NULL) {
     return(aesthetics)
   }
 
-  element <- calc_element("geom", theme) %||% .default_geom_element
+  el <- calc_element("geom", theme) %||% .default_geom_element
   class <- setdiff(class, c("Geom", "ggproto", "gg"))
 
   if (length(class) > 0) {
@@ -260,12 +260,12 @@ eval_from_theme <- function(aesthetics, theme, class = NULL) {
     # Inherit up to parent geom class
     if (length(class) > 0) {
       for (cls in rev(class)) {
-        element <- combine_elements(theme[[cls]], element)
+        el <- combine_elements(theme[[cls]], el)
       }
     }
   }
 
-  lapply(aesthetics[themed], eval_tidy, data = element)
+  lapply(aesthetics[themed], eval_tidy, data = S7::props(el))
 }
 
 #' Graphical units
diff --git a/R/geom-label.R b/R/geom-label.R
index a9d288996f..652ae9b39b 100644
--- a/R/geom-label.R
+++ b/R/geom-label.R
@@ -88,7 +88,7 @@ GeomLabel <- ggproto("GeomLabel", Geom,
     data <- coord$transform(data, panel_params)
     data$vjust <- compute_just(data$vjust, data$y, data$x, data$angle)
     data$hjust <- compute_just(data$hjust, data$x, data$y, data$angle)
-    if (!is_margin("margin")) {
+    if (!is_margin(label.padding)) {
       label.padding <- rep(label.padding, length.out = 4)
     }
 
diff --git a/R/guide-.R b/R/guide-.R
index 8d26a95628..a888659cf1 100644
--- a/R/guide-.R
+++ b/R/guide-.R
@@ -376,6 +376,7 @@ Guide <- ggproto(
   # Renders tickmarks
   build_ticks = function(key, elements, params, position = params$position,
                          length = elements$ticks_length) {
+    force(length)
     if (!is_theme_element(elements)) {
       elements <- elements$ticks
     }
diff --git a/R/guide-axis-logticks.R b/R/guide-axis-logticks.R
index 37273cba06..9da147870d 100644
--- a/R/guide-axis-logticks.R
+++ b/R/guide-axis-logticks.R
@@ -119,7 +119,7 @@ guide_axis_logticks <- function(
     allow_null = TRUE
   )
   check_bool(expanded)
-  check_inherits(short.theme, c("element_blank", "element_line"))
+  check_inherits(short.theme, c("ggplot2::element_blank", "ggplot2::element_line"))
 
   new_guide(
     available_aes  = c("x", "y"),
diff --git a/R/guide-axis-theta.R b/R/guide-axis-theta.R
index 5183e802fc..b75528d347 100644
--- a/R/guide-axis-theta.R
+++ b/R/guide-axis-theta.R
@@ -154,7 +154,7 @@ GuideAxisTheta <- ggproto(
     }
 
     offset <- max(unit(0, "pt"), elements$major_length, elements$minor_length)
-    elements$offset <- offset + max(elements$text$margin %||% unit(0, "pt"))
+    elements$offset <- offset + max(elements$text@margin %||% unit(0, "pt"))
     elements
   },
 
@@ -184,7 +184,7 @@ GuideAxisTheta <- ggproto(
 
   build_labels = function(key, elements, params) {
 
-    if (inherits(elements$text, "element_blank")) {
+    if (is_theme_element(elements$text, "blank")) {
       return(zeroGrob())
     }
 
@@ -198,7 +198,7 @@ GuideAxisTheta <- ggproto(
 
     # Resolve text angle
     if (is.waiver(params$angle) || is.null(params$angle)) {
-      angle <- elements$text$angle
+      angle <- elements$text@angle
     } else {
       angle <- flip_text_angle(params$angle - rad2deg(key$theta))
     }
@@ -268,20 +268,20 @@ GuideAxisTheta <- ggproto(
     key <- params$key
     key <- vec_slice(key, !is.na(key$.label) & nzchar(key$.label))
     labels <- validate_labels(key$.label)
-    if (length(labels) == 0 || inherits(elements$text, "element_blank")) {
+    if (length(labels) == 0 || is_theme_element(elements$text, "blank")) {
       return(list(offset = offset))
     }
 
     # Resolve text angle
     if (is.waiver(params$angle %||% waiver())) {
-      angle <- elements$text$angle
+      angle <- elements$text@angle
     } else {
       angle <- flip_text_angle(params$angle - rad2deg(key$theta))
     }
     angle <- key$theta + deg2rad(angle)
 
     # Set margin
-    margin <- rep(max(elements$text$margin), length.out = 4)
+    margin <- rep(max(elements$text@margin), length.out = 4)
 
     # Measure size of each individual label
     single_labels <- lapply(labels, function(lab) {
@@ -365,7 +365,7 @@ GuideAxisTheta <- ggproto(
 
 theta_tickmarks <- function(key, element, length, offset = NULL) {
   n_breaks <- nrow(key)
-  if (n_breaks < 1 || inherits(element, "element_blank")) {
+  if (n_breaks < 1 || is_theme_element(element, "blank")) {
     return(zeroGrob())
   }
 
diff --git a/R/guide-axis.R b/R/guide-axis.R
index d445900071..03dffcaebd 100644
--- a/R/guide-axis.R
+++ b/R/guide-axis.R
@@ -259,10 +259,10 @@ GuideAxis <- ggproto(
   override_elements = function(params, elements, theme) {
     elements$text <-
       label_angle_heuristic(elements$text, params$position, params$angle)
-    if (inherits(elements$ticks, "element_blank")) {
+    if (is_theme_element(elements$ticks, "blank")) {
       elements$major_length <- unit(0, "cm")
     }
-    if (inherits(elements$minor, "element_blank") || isFALSE(params$minor.ticks)) {
+    if (is_theme_element(elements$minor, "blank") || isFALSE(params$minor.ticks)) {
       elements$minor_length <- unit(0, "cm")
     }
     return(elements)
@@ -379,7 +379,7 @@ GuideAxis <- ggproto(
     # Ticks
     major_cm <- convertUnit(elements$major_length, "cm", valueOnly = TRUE)
     range <- range(0, major_cm)
-    if (params$minor.ticks && !inherits(elements$minor, "element_blank")) {
+    if (params$minor.ticks && !is_theme_element(elements$minor, "blank")) {
       minor_cm <- convertUnit(elements$minor_length, "cm", valueOnly = TRUE)
       range <- range(range, minor_cm)
     }
@@ -450,13 +450,13 @@ GuideAxis <- ggproto(
     # rather than dimensions of this axis alone.
     if (has_labels && params$position %in% c("left", "right")) {
       where <- layout$l[-c(1, length(layout$l))]
-      just <- with(elements$text, rotate_just(angle, hjust, vjust))$hjust %||% 0.5
+      just <- with(S7::props(elements$text), rotate_just(angle, hjust, vjust))$hjust %||% 0.5
       gt <- gtable_add_cols(gt, unit(just, "null"), pos = min(where) - 1)
       gt <- gtable_add_cols(gt, unit(1 - just, "null"), pos = max(where) + 1)
     }
     if (has_labels && params$position %in% c("top", "bottom")) {
       where <- layout$t[-c(1, length(layout$t))]
-      just <- with(elements$text, rotate_just(angle, hjust, vjust))$vjust %||% 0.5
+      just <- with(S7::props(elements$text), rotate_just(angle, hjust, vjust))$vjust %||% 0.5
       gt <- gtable_add_rows(gt, unit(1 - just, "null"), pos = min(where) - 1)
       gt <- gtable_add_rows(gt, unit(just, "null"), pos = max(where) + 1)
     }
@@ -590,7 +590,7 @@ axis_label_priority_between <- function(x, y) {
 #'   overridden from the user- or theme-supplied element.
 #' @noRd
 label_angle_heuristic <- function(element, position, angle) {
-  if (!inherits(element, "element_text")
+  if (!is_theme_element(element, "text")
       || is.null(position)
       || is.null(angle %|W|% NULL)) {
     return(element)
@@ -612,8 +612,8 @@ label_angle_heuristic <- function(element, position, angle) {
   hjust <- switch(position, left = cosine, right = 1 - cosine, top = 1 - sine, sine)
   vjust <- switch(position, left = 1 - sine, right = sine, top = 1 - cosine, cosine)
 
-  element$angle <- angle %||% element$angle
-  element$hjust <- hjust %||% element$hjust
-  element$vjust <- vjust %||% element$vjust
+  element@angle <- angle %||% element@angle
+  element@hjust <- hjust %||% element@hjust
+  element@vjust <- vjust %||% element@vjust
   element
 }
diff --git a/R/guide-custom.R b/R/guide-custom.R
index f602bfc843..1a6d977c7f 100644
--- a/R/guide-custom.R
+++ b/R/guide-custom.R
@@ -113,7 +113,7 @@ GuideCustom <- ggproto(
 
     gt <- self$add_title(
       gt, title, title_position,
-      with(elems$title, rotate_just(angle, hjust, vjust))
+      with(S7::props(elems$title), rotate_just(angle, hjust, vjust))
     )
 
     # Add padding and background
diff --git a/R/guide-legend.R b/R/guide-legend.R
index b728752518..294c573725 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -325,7 +325,7 @@ GuideLegend <- ggproto(
     # Resolve title. The trick here is to override the main text element, so
     # that any settings declared in `legend.title` will be honoured but we have
     # custom defaults for the guide.
-    margin <- calc_element("text", theme)$margin
+    margin <- calc_element("text", theme)@margin
     title <- theme(text = element_text(
       hjust = 0, vjust = 0.5,
       margin = position_margin(title_position, margin, gap)
@@ -573,7 +573,7 @@ GuideLegend <- ggproto(
 
     gt <- self$add_title(
       gt, grobs$title, elements$title_position,
-      with(elements$title, rotate_just(angle, hjust, vjust))
+      with(S7::props(elements$title), rotate_just(angle, hjust, vjust))
     )
 
     gt <- gtable_add_padding(gt, unit(elements$padding, "cm"))
@@ -690,13 +690,17 @@ keep_key_data <- function(key, data, aes, show) {
 
 position_margin <- function(position, margin = NULL, gap = unit(0, "pt")) {
   margin <- margin %||% margin()
-  switch(
+  margin <- switch(
     position,
     top    = replace(margin, 3, margin[3] + gap),
     bottom = replace(margin, 1, margin[1] + gap),
     left   = replace(margin, 2, margin[2] + gap),
     right  = replace(margin, 4, margin[4] + gap)
   )
+  # We have to manually reconstitute the class because the 'simpleUnit' class
+  # might be dropped by the replacement operation.
+  class(margin) <- c("ggplot2::margin", class(margin), "S7_object")
+  margin
 }
 
 # Function implementing backward compatibility with the old way of specifying
diff --git a/R/guides-.R b/R/guides-.R
index d96ef16074..a875a845fd 100644
--- a/R/guides-.R
+++ b/R/guides-.R
@@ -828,7 +828,7 @@ get_guide_data <- function(plot = get_last_plot(), aesthetic, panel = 1L) {
 
   if (!aesthetic %in% c("x", "y", "x.sec", "y.sec", "theta", "r")) {
     # Non position guides: check if aesthetic in colnames of key
-    keys <- lapply(plot$plot$guides$params, `[[`, "key")
+    keys <- lapply(plot@plot@guides$params, `[[`, "key")
     keep <- vapply(keys, function(x) any(colnames(x) %in% aesthetic), logical(1))
     keys <- switch(sum(keep) + 1, NULL, keys[[which(keep)]], keys[keep])
     return(keys)
@@ -836,12 +836,12 @@ get_guide_data <- function(plot = get_last_plot(), aesthetic, panel = 1L) {
 
   # Position guides: find the right layout entry
   check_number_whole(panel)
-  layout <- plot$layout$layout
+  layout <- plot@layout$layout
   select <- layout[layout$PANEL == panel, , drop = FALSE]
   if (nrow(select) == 0) {
     return(NULL)
   }
-  params <- plot$layout$panel_params[select$PANEL][[1]]
+  params <- plot@layout$panel_params[select$PANEL][[1]]
 
   # If panel params don't have guides, we probably have old coord system
   # that doesn't use the guide system.
diff --git a/R/labels.R b/R/labels.R
index 27c1e96de6..ef31a8fb07 100644
--- a/R/labels.R
+++ b/R/labels.R
@@ -12,7 +12,7 @@
 #' update_labels(p, list(colour = "Fail silently"))
 update_labels <- function(p, labels) {
   p <- plot_clone(p)
-  p$labels <- defaults(labels, p$labels)
+  p@labels <- labs(!!!defaults(labels, p@labels))
   p
 }
 
@@ -26,7 +26,7 @@ setup_plot_labels <- function(plot, layers, data) {
     layer <- layers[[i]]
 
     mapping <- layer$computed_mapping
-    if (inherits(mapping, "unlabelled_uneval")) {
+    if (inherits(mapping, "unlabelled")) {
       next
     }
 
@@ -75,7 +75,7 @@ setup_plot_labels <- function(plot, layers, data) {
   # Warn for spurious labels that don't have a mapping.
   # Note: sometimes, 'x' and 'y' might not have a mapping, like in
   # `geom_function()`. We can display these labels anyway, so we include them.
-  plot_labels  <- plot$labels
+  plot_labels  <- plot@labels
   known_labels <- c(names(labels), fn_fmls_names(labs), "x", "y")
   extra_labels <- setdiff(names(plot_labels), known_labels)
 
@@ -108,7 +108,7 @@ setup_plot_labels <- function(plot, layers, data) {
     })
   }
 
-  defaults(plot_labels, labels)
+  labs(!!!defaults(plot_labels, labels))
 }
 
 #' Modify axis, legend, and plot labels
@@ -181,21 +181,20 @@ setup_plot_labels <- function(plot, layers, data) {
 #' p +
 #'  labs(title = "title") +
 #'  labs(title = NULL)
-labs <- function(..., title = waiver(), subtitle = waiver(), caption = waiver(),
-                 tag = waiver(), dictionary = waiver(), alt = waiver(),
-                 alt_insight = waiver()) {
+labs <- function(..., title = waiver(), subtitle = waiver(),
+                 caption = waiver(), tag = waiver(), dictionary = waiver(),
+                 alt = waiver(), alt_insight = waiver()) {
   # .ignore_empty = "all" is needed to allow trailing commas, which is NOT a trailing comma for dots_list() as it's in ...
   args <- dots_list(..., title = title, subtitle = subtitle, caption = caption,
-    tag = tag, alt = allow_lambda(alt), alt_insight = alt_insight,
-    dictionary = dictionary, .ignore_empty = "all")
+                    tag = tag, alt = allow_lambda(alt), alt_insight = alt_insight,
+                    dictionary = dictionary, .ignore_empty = "all")
 
   is_waive <- vapply(args, is.waiver, logical(1))
   args <- args[!is_waive]
   # remove duplicated arguments
   args <- args[!duplicated(names(args))]
   args <- rename_aes(args)
-
-  structure(args, class = c("labels", "gg"))
+  class_labels(args)
 }
 
 #' @rdname labs
@@ -224,18 +223,18 @@ ggtitle <- function(label, subtitle = waiver()) {
 get_labs <- function(plot = get_last_plot()) {
   plot <- ggplot_build(plot)
 
-  labs <- plot$plot$labels
+  labs <- plot@plot@labels
 
   xy_labs <- rename(
-    c(x = plot$layout$resolve_label(plot$layout$panel_scales_x[[1]], labs),
-      y = plot$layout$resolve_label(plot$layout$panel_scales_y[[1]], labs)),
+    c(x = plot@layout$resolve_label(plot@layout$panel_scales_x[[1]], labs),
+      y = plot@layout$resolve_label(plot@layout$panel_scales_y[[1]], labs)),
     c(x.primary = "x", x.secondary = "x.sec",
       y.primary = "y", y.secondary = "y.sec")
   )
 
   labs <- defaults(xy_labs, labs)
 
-  guides <- plot$plot$guides
+  guides <- plot@plot@guides
   if (length(guides$aesthetics) == 0) {
     return(labs)
   }
@@ -279,29 +278,29 @@ get_labs <- function(plot = get_last_plot()) {
 #'
 #' get_alt_text(p)
 #'
-get_alt_text <- function(p, ...) {
+get_alt_text <- S7::new_generic("get_alt_text", "p", fun = function(p, ...) {
   warn_dots_used()
-  UseMethod("get_alt_text")
-}
-#' @export
-get_alt_text.ggplot <- function(p, ...) {
-  alt <- p$labels[["alt"]] %||% ""
+  S7::S7_dispatch()
+})
+
+S7::method(get_alt_text, class_ggplot) <- function(p, ...) {
+  alt <- p@labels[["alt"]] %||% ""
   if (!is.function(alt)) {
     return(alt)
   }
-  p$labels[["alt"]] <- NULL
+  p@labels[["alt"]] <- NULL
   build <- ggplot_build(p)
-  build$plot$labels[["alt"]] <- alt
+  build@plot@labels[["alt"]] <- alt
   get_alt_text(build)
 }
-#' @export
-get_alt_text.ggplot_built <- function(p, ...) {
-  alt <- p$plot$labels[["alt"]] %||% ""
-  p$plot$labels[["alt"]] <- NULL
-  if (is.function(alt)) alt(p$plot) else alt
+
+S7::method(get_alt_text, class_ggplot_built) <- function(p, ...) {
+  alt <- p@plot@labels[["alt"]] %||% ""
+  p@plot@labels[["alt"]] <- NULL
+  if (is.function(alt)) alt(p@plot) else alt
 }
-#' @export
-get_alt_text.gtable <- function(p, ...) {
+
+S7::method(get_alt_text, class_gtable) <- function(p, ...) {
   attr(p, "alt-label") %||% ""
 }
 
@@ -351,8 +350,8 @@ get_alt_text.gtable <- function(p, ...) {
 #'
 generate_alt_text <- function(p) {
   # Combine titles
-  if (!is.null(p$label$title %||% p$labels$subtitle)) {
-    title <- sub("\\.?$", "", c(p$labels$title, p$labels$subtitle))
+  if (!is.null(p@labels$title %||% p@labels$subtitle)) {
+    title <- sub("\\.?$", "", c(p@labels$title, p@labels$subtitle))
     if (length(title) == 2) {
       title <- paste0(title[1], ": ", title[2])
     }
@@ -368,7 +367,7 @@ generate_alt_text <- function(p) {
   axes <- safe_string(axes)
 
   # Get layer types
-  layers <- vapply(p$layers, function(l) snake_class(l$geom), character(1))
+  layers <- vapply(p@layers, function(l) snake_class(l$geom), character(1))
   layers <- sub("_", " ", sub("^geom_", "", unique0(layers)))
   if (length(layers) == 1) {
     layers <- paste0(" using a ", layers, " layer")
@@ -379,8 +378,8 @@ generate_alt_text <- function(p) {
 
   # Combine
   alt <- paste0(title, "A plot", axes, layers, ".")
-  if (!is.null(p$labels$alt_insight)) {
-    alt <- paste0(alt, " ", p$labels$alt_insight)
+  if (!is.null(p@labels$alt_insight)) {
+    alt <- paste0(alt, " ", p@labels$alt_insight)
   }
   as.character(alt)
 }
@@ -388,12 +387,12 @@ safe_string <- function(string) {
   if (length(string) == 0) "" else string
 }
 scale_description <- function(p, name) {
-  scale <- p$scales$get_scales(name)
+  scale <- p@scales$get_scales(name)
   if (is.null(scale)) {
-    lab <- p$labels[[name]]
+    lab <- p@labels[[name]]
     type <- "the"
   } else {
-    lab <- scale$make_title(scale$name %|W|% p$labels[[name]])
+    lab <- scale$make_title(scale$name %|W|% p@labels[[name]])
     type <- "a continuous"
     if (scale$is_discrete()) type <- "a discrete"
     if (inherits(scale, "ScaleBinned")) type <- "a binned"
diff --git a/R/layer-sf.R b/R/layer-sf.R
index 3a282e734f..7a952971ec 100644
--- a/R/layer-sf.R
+++ b/R/layer-sf.R
@@ -45,7 +45,7 @@ LayerSf <- ggproto("LayerSf", Layer,
     # automatically determine the name of the geometry column
     # and add the mapping if it doesn't exist
     if ((isTRUE(self$inherit.aes) && is.null(self$computed_mapping$geometry) &&
-         is.null(plot$computed_mapping$geometry)) ||
+         is.null(self$computed_mapping$geometry)) ||
         (!isTRUE(self$inherit.aes) && is.null(self$computed_mapping$geometry))) {
       if (is_sf(data)) {
         geometry_col <- attr(data, "sf_column")
diff --git a/R/layer.R b/R/layer.R
index b1029579bc..f5abbd3a60 100644
--- a/R/layer.R
+++ b/R/layer.R
@@ -204,7 +204,7 @@ validate_mapping <- function(mapping, call = caller_env()) {
     msg <- "{.arg mapping} must be created by {.fn aes}."
     # Native pipe have higher precedence than + so any type of gg object can be
     # expected here, not just ggplot
-    if (inherits(mapping, "gg")) {
+    if (S7::S7_inherits(mapping, class_gg)) {
       msg <- c(msg, "i" = "Did you use {.code %>%} or {.code |>} instead of {.code +}?")
     }
 
@@ -214,7 +214,7 @@ validate_mapping <- function(mapping, call = caller_env()) {
   }
 
   # For backward compatibility with pre-tidy-eval layers
-  new_aes(mapping)
+  class_mapping(mapping)
 }
 
 Layer <- ggproto("Layer", NULL,
@@ -266,18 +266,16 @@ Layer <- ggproto("Layer", NULL,
   setup_layer = function(self, data, plot) {
     # For annotation geoms, it is useful to be able to ignore the default aes
     if (isTRUE(self$inherit.aes)) {
-      self$computed_mapping <- defaults(self$mapping, plot$mapping)
+      self$computed_mapping <- class_mapping(defaults(self$mapping, plot@mapping))
 
       # Inherit size as linewidth from global mapping
       if (self$geom$rename_size &&
-          "size" %in% names(plot$mapping) &&
+          "size" %in% names(plot@mapping) &&
           !"linewidth" %in% names(self$computed_mapping) &&
           "linewidth" %in% self$geom$aesthetics()) {
-        self$computed_mapping$size <- plot$mapping$size
+        self$computed_mapping$size <- plot@mapping$size
         deprecate_warn0("3.4.0", I("Using `size` aesthetic for lines"), I("`linewidth`"))
       }
-      # defaults() strips class, but it needs to be preserved for now
-      class(self$computed_mapping) <- "uneval"
     } else {
       self$computed_mapping <- self$mapping
     }
@@ -304,7 +302,7 @@ Layer <- ggproto("Layer", NULL,
 
     # Evaluate aesthetics
     evaled <- eval_aesthetics(aesthetics, data)
-    plot$scales$add_defaults(evaled, plot$plot_env)
+    plot@scales$add_defaults(evaled, plot@plot_env)
 
     # Check for discouraged usage in mapping
     warn_for_aes_extract_usage(aesthetics, data[setdiff(names(data), "PANEL")])
@@ -375,7 +373,7 @@ Layer <- ggproto("Layer", NULL,
     if (length(new) == 0) return(data)
 
     # data needs to be non-scaled
-    data_orig <- plot$scales$backtransform_df(data)
+    data_orig <- plot@scales$backtransform_df(data)
 
     # Add map stat output to aesthetics
     stat_data <- eval_aesthetics(
@@ -392,11 +390,11 @@ Layer <- ggproto("Layer", NULL,
     stat_data <- data_frame0(!!!stat_data)
 
     # Add any new scales, if needed
-    plot$scales$add_defaults(stat_data, plot$plot_env)
+    plot@scales$add_defaults(stat_data, plot@plot_env)
     # Transform the values, if the scale say it's ok
     # (see stat_spoke for one exception)
     if (self$stat$retransform) {
-      stat_data <- plot$scales$transform_df(stat_data)
+      stat_data <- plot@scales$transform_df(stat_data)
     }
     stat_data <- cleanup_mismatched_data(stat_data, nrow(data), "after_stat")
     data[names(stat_data)] <- stat_data
diff --git a/R/margins.R b/R/margins.R
index 561aefb7bd..a010a87738 100644
--- a/R/margins.R
+++ b/R/margins.R
@@ -1,17 +1,21 @@
+#' @include properties.R
+
 #' @param t,r,b,l Dimensions of each margin. (To remember order, think trouble).
 #' @param unit Default units of dimensions. Defaults to "pt" so it
 #'   can be most easily scaled with the text.
 #' @rdname element
 #' @export
-margin <- function(t = 0, r = 0, b = 0, l = 0, unit = "pt") {
-  u <- unit(c(t, r, b, l), unit)
-  class(u) <- c("margin", class(u))
-  u
-}
+margin <- S7::new_class(
+  "margin", parent = S7::new_S3_class(c("simpleUnit", "unit", "unit_v2")),
+  constructor = function(t = 0, r = 0, b = 0, l = 0, unit = "pt") {
+    u <- unit(c(t, r, b, l), unit)
+    S7::new_object(u)
+  }
+)
 
 #' @export
 #' @rdname is_tests
-is_margin <- function(x) inherits(x, "margin")
+is_margin <- function(x) S7::S7_inherits(x, margin)
 is.margin <- function(x) lifecycle::deprecate_stop("3.5.2", "is.margin()", "is_margin()")
 
 #' @rdname element
diff --git a/R/plot-build.R b/R/plot-build.R
index 24644951c2..a8fd5498cc 100644
--- a/R/plot-build.R
+++ b/R/plot-build.R
@@ -23,44 +23,42 @@
 #' The `r link_book("build step section", "internals#sec-ggplotbuild")`
 #' @keywords internal
 #' @export
-ggplot_build <- function(plot) {
+ggplot_build <- S7::new_generic("ggplot_build", "plot", fun = function(plot) {
   # Attaching the plot env to be fetched by deprecations etc.
-  attach_plot_env(plot$plot_env)
-
-  UseMethod('ggplot_build')
-}
+  if (S7::S7_inherits(plot) && S7::prop_exists(plot, "plot_env")) {
+    attach_plot_env(plot@plot_env)
+  }
+  S7::S7_dispatch()
+})
 
-#' @export
-ggplot_build.ggplot_built <- function(plot) {
-  # This is a no-op
-  plot
+S7::method(ggplot_build, class_ggplot_built) <- function(plot) {
+  plot # This is a no-op
 }
 
-#' @export
-ggplot_build.ggplot <- function(plot) {
+S7::method(ggplot_build, class_ggplot) <- function(plot) {
   plot <- plot_clone(plot)
-  if (length(plot$layers) == 0) {
+  if (length(plot@layers) == 0) {
     plot <- plot + geom_blank()
   }
 
-  layers <- plot$layers
+  layers <- plot@layers
   data <- rep(list(NULL), length(layers))
 
-  scales <- plot$scales
+  scales <- plot@scales
 
   # Allow all layers to make any final adjustments based
   # on raw input data and plot info
-  data <- by_layer(function(l, d) l$layer_data(plot$data), layers, data, "computing layer data")
+  data <- by_layer(function(l, d) l$layer_data(plot@data), layers, data, "computing layer data")
   data <- by_layer(function(l, d) l$setup_layer(d, plot), layers, data, "setting up layer")
 
   # Initialise panels, add extra data for margins & missing faceting
   # variables, and add on a PANEL variable to data
-  layout <- create_layout(plot$facet, plot$coordinates, plot$layout)
-  data <- layout$setup(data, plot$data, plot$plot_env)
+  layout <- create_layout(plot@facet, plot@coordinates, plot@layout)
+  data <- layout$setup(data, plot@data, plot@plot_env)
 
   # Compute aesthetics to produce data with generalised variable names
   data <- by_layer(function(l, d) l$compute_aesthetics(d, plot), layers, data, "computing aesthetics")
-  plot$labels <- setup_plot_labels(plot, layers, data)
+  plot@labels <- setup_plot_labels(plot, layers, data)
   data <- .ignore_data(data)
 
   # Transform all scales
@@ -80,7 +78,7 @@ ggplot_build.ggplot <- function(plot) {
   data <- by_layer(function(l, d) l$map_statistic(d, plot), layers, data, "mapping stat to aesthetics")
 
   # Make sure missing (but required) aesthetics are added
-  plot$scales$add_missing(c("x", "y"), plot$plot_env)
+  plot@scales$add_missing(c("x", "y"), plot@plot_env)
 
   # Reparameterise geoms from (e.g.) y and width to ymin and ymax
   data <- by_layer(function(l, d) l$compute_geom_1(d), layers, data, "setting up geom")
@@ -98,27 +96,27 @@ ggplot_build.ggplot <- function(plot) {
   data <- layout$map_position(data)
 
   # Hand off position guides to layout
-  layout$setup_panel_guides(plot$guides, plot$layers)
+  layout$setup_panel_guides(plot@guides, plot@layers)
 
   # Complete the plot's theme
-  plot$theme <- plot_theme(plot)
+  plot@theme <- plot_theme(plot)
 
   # Train and map non-position scales and guides
   npscales <- scales$non_position_scales()
   if (npscales$n() > 0) {
-    npscales$set_palettes(plot$theme)
+    npscales$set_palettes(plot@theme)
     lapply(data, npscales$train_df)
-    plot$guides <- plot$guides$build(npscales, plot$layers, plot$labels, data, plot$theme)
+    plot@guides <- plot@guides$build(npscales, plot@layers, plot@labels, data, plot@theme)
     data <- lapply(data, npscales$map_df)
   } else {
     # Only keep custom guides if there are no non-position scales
-    plot$guides <- plot$guides$get_custom()
+    plot@guides <- plot@guides$get_custom()
   }
   data <- .expose_data(data)
 
   # Fill in defaults etc.
   data <- by_layer(
-    function(l, d) l$compute_geom_2(d, theme = plot$theme),
+    function(l, d) l$compute_geom_2(d, theme = plot@theme),
     layers, data, "setting up geom aesthetics"
   )
 
@@ -129,18 +127,15 @@ ggplot_build.ggplot <- function(plot) {
   data <- layout$finish_data(data)
 
   # Consolidate alt-text
-  plot$labels$alt <- get_alt_text(plot)
+  plot@labels$alt <- get_alt_text(plot)
 
-  structure(
-    list(data = data, layout = layout, plot = plot),
-    class = "ggplot_built"
-  )
+  class_ggplot_built(data = data, layout = layout, plot = plot)
 }
 
 #' @export
 #' @rdname ggplot_build
 get_layer_data <- function(plot = get_last_plot(), i = 1L) {
-  ggplot_build(plot)$data[[i]]
+  ggplot_build(plot)@data[[i]]
 }
 #' @export
 #' @rdname ggplot_build
@@ -151,12 +146,12 @@ layer_data <- get_layer_data
 get_panel_scales <- function(plot = get_last_plot(), i = 1L, j = 1L) {
   b <- ggplot_build(plot)
 
-  layout <- b$layout$layout
+  layout <- b@layout$layout
   selected <- layout[layout$ROW == i & layout$COL == j, , drop = FALSE]
 
   list(
-    x = b$layout$panel_scales_x[[selected$SCALE_X]],
-    y = b$layout$panel_scales_y[[selected$SCALE_Y]]
+    x = b@layout$panel_scales_x[[selected$SCALE_X]],
+    y = b@layout$panel_scales_y[[selected$SCALE_Y]]
   )
 }
 
@@ -169,7 +164,7 @@ layer_scales <- get_panel_scales
 get_layer_grob <- function(plot = get_last_plot(), i = 1L) {
   b <- ggplot_build(plot)
 
-  b$plot$layers[[i]]$draw_geom(b$data[[i]], b$layout)
+  b@plot@layers[[i]]$draw_geom(b@data[[i]], b@layout)
 }
 
 #' @export
@@ -194,45 +189,42 @@ layer_grob <- get_layer_grob
 #' @keywords internal
 #' @param data plot data generated by [ggplot_build()]
 #' @export
-ggplot_gtable <- function(data) {
-  # Attaching the plot env to be fetched by deprecations etc.
-  attach_plot_env(data$plot$plot_env)
+ggplot_gtable <- S7::new_generic("ggplot_gtable", "data", function(data) {
+  attach_plot_env(data@plot@plot_env)
+  S7::S7_dispatch()
+})
 
-  UseMethod('ggplot_gtable')
-}
-
-#' @export
-ggplot_gtable.ggplot_built <- function(data) {
-  plot <- data$plot
-  layout <- data$layout
-  data <- data$data
-  theme <- plot$theme
+S7::method(ggplot_gtable, class_ggplot_built) <- function(data) {
+  plot <- data@plot
+  layout <- data@layout
+  data <- data@data
+  theme <- plot@theme
 
-  geom_grobs <- by_layer(function(l, d) l$draw_geom(d, layout), plot$layers, data, "converting geom to grob")
+  geom_grobs <- by_layer(function(l, d) l$draw_geom(d, layout), plot@layers, data, "converting geom to grob")
 
-  plot_table <- layout$render(geom_grobs, data, theme, plot$labels)
+  plot_table <- layout$render(geom_grobs, data, theme, plot@labels)
 
   # Legends
-  legend_box <- plot$guides$assemble(theme)
+  legend_box <- plot@guides$assemble(theme)
   plot_table <- table_add_legends(plot_table, legend_box, theme)
 
   # Title
   title <- element_render(
-    theme, "plot.title", plot$labels$title,
+    theme, "plot.title", plot@labels$title,
     margin_y = TRUE, margin_x = TRUE
   )
   title_height <- grobHeight(title)
 
   # Subtitle
   subtitle <- element_render(
-    theme, "plot.subtitle", plot$labels$subtitle,
+    theme, "plot.subtitle", plot@labels$subtitle,
     margin_y = TRUE, margin_x = TRUE
   )
   subtitle_height <- grobHeight(subtitle)
 
   # whole plot annotation
   caption <- element_render(
-    theme, "plot.caption", plot$labels$caption,
+    theme, "plot.caption", plot@labels$caption,
     margin_y = TRUE, margin_x = TRUE
   )
   caption_height <- grobHeight(caption)
@@ -283,7 +275,7 @@ ggplot_gtable.ggplot_built <- function(data) {
   plot_table <- gtable_add_grob(plot_table, caption, name = "caption",
     t = -1, b = -1, l = caption_l, r = caption_r, clip = "off")
 
-  plot_table <- table_add_tag(plot_table, plot$labels$tag, theme)
+  plot_table <- table_add_tag(plot_table, plot@labels$tag, theme)
 
   # Margins
   plot_margin <- calc_element("plot.margin", theme) %||% margin()
@@ -298,7 +290,7 @@ ggplot_gtable.ggplot_built <- function(data) {
   }
 
   # add alt-text as attribute
-  attr(plot_table, "alt-label") <- plot$labels$alt
+  attr(plot_table, "alt-label") <- plot@labels$alt
 
   plot_table
 }
@@ -312,11 +304,8 @@ ggplotGrob <- function(x) {
   ggplot_gtable(ggplot_build(x))
 }
 
-#' @export
-as.gtable.ggplot <- function(x, ...) ggplotGrob(x)
-
-#' @export
-as.gtable.ggplot_built <- function(x, ...) ggplot_gtable(x)
+S7::method(as.gtable, class_ggplot) <- function(x, ...) ggplotGrob(x)
+S7::method(as.gtable, class_ggplot_built) <- function(x, ...) ggplot_gtable(x)
 
 # Apply function to layer and matching data
 by_layer <- function(f, layers, data, step = NULL) {
@@ -348,7 +337,7 @@ table_add_tag <- function(table, label, theme) {
     return(table)
   }
   element <- calc_element("plot.tag", theme)
-  if (inherits(element, "element_blank")) {
+  if (is_theme_element(element, "blank")) {
     return(table)
   }
 
@@ -393,20 +382,20 @@ table_add_tag <- function(table, label, theme) {
   if (location %in% c("plot", "panel")) {
     if (!is.numeric(position)) {
       if (right || left) {
-        x <- (1 - element$hjust) * width
+        x <- (1 - element@hjust) * width
         if (right) {
           x <- unit(1, "npc") - x
         }
       } else {
-        x <- unit(element$hjust, "npc")
+        x <- unit(element@hjust, "npc")
       }
       if (top || bottom) {
-        y <- (1 - element$vjust) * height
+        y <- (1 - element@vjust) * height
         if (top) {
           y <- unit(1, "npc") - y
         }
       } else {
-        y <- unit(element$vjust, "npc")
+        y <- unit(element@vjust, "npc")
       }
     } else {
       x <- unit(position[1], "npc")
diff --git a/R/plot-construction.R b/R/plot-construction.R
index b10a9f4387..5d9b550812 100644
--- a/R/plot-construction.R
+++ b/R/plot-construction.R
@@ -24,8 +24,6 @@
 #' @param e1 An object of class [ggplot()] or a [theme()].
 #' @param e2 A plot component, as described below.
 #' @seealso [theme()]
-#' @export
-#' @method + gg
 #' @rdname gg-add
 #' @examples
 #' base <-
@@ -39,7 +37,7 @@
 #' # Alternatively, you can add multiple components with a list.
 #' # This can be useful to return from a function.
 #' base + list(subset(mpg, fl == "p"), geom_smooth())
-"+.gg" <- function(e1, e2) {
+add_gg <- function(e1, e2) {
   if (missing(e2)) {
     cli::cli_abort(c(
             "Cannot use {.code +} with a single argument.",
@@ -52,6 +50,7 @@
   e2name <- deparse(substitute(e2))
 
   if      (is_theme(e1))  add_theme(e1, e2, e2name)
+  # The `add_ggplot()` branch here is for backward compatibility with R < 4.3.0
   else if (is_ggplot(e1)) add_ggplot(e1, e2, e2name)
   else if (is_ggproto(e1)) {
     cli::cli_abort(c(
@@ -61,10 +60,30 @@
   }
 }
 
+if (getRversion() < "4.3.0") {
+  S7::method(`+`, list(class_S3_gg, S7::class_any)) <- add_gg
+}
+
+S7::method(`+`, list(class_ggplot, S7::class_any)) <- function(e1, e2) {
+  e2name <- deparse(substitute(e2, env = caller_env(2)))
+  add_ggplot(e1, e2, e2name)
+}
+
+S7::method(`+`, list(class_theme, S7::class_any)) <- function(e1, e2) {
+  e2name <- deparse(substitute(e2, env = caller_env(2)))
+  add_theme(e1, e2, e2name)
+}
+
 
 #' @rdname gg-add
 #' @export
-"%+%" <- `+.gg`
+"%+%" <- function(e1, e2) {
+  if (getRversion() < "4.3.0") {
+    add_gg(e1, e2)
+  } else {
+    `+`(e1, e2)
+  }
+}
 
 add_ggplot <- function(p, object, objectname) {
   if (is.null(object)) return(p)
@@ -77,11 +96,10 @@ add_ggplot <- function(p, object, objectname) {
 #' Add custom objects to ggplot
 #'
 #' This generic allows you to add your own methods for adding custom objects to
-#' a ggplot with [+.gg].
+#' a ggplot with [+.gg][add_gg].
 #'
 #' @param object An object to add to the plot
 #' @param plot The ggplot object to add `object` to
-#' @param object_name The name of the object to add
 #'
 #' @return A modified ggplot object
 #' @details
@@ -98,10 +116,11 @@ add_ggplot <- function(p, object, objectname) {
 #' @export
 #' @examples
 #' # making a new method for the generic
-#' # in this example, we apply a text element to the text theme setting
-#' ggplot_add.element_text <- function(object, plot, object_name) {
-#'   plot + theme(text = object)
-#' }
+#' # in this example, we enable adding text elements
+#' S7::method(ggplot_add, list(element_text, class_ggplot)) <-
+#'   function(object, plot, ...) {
+#'     plot + theme(text = object)
+#'   }
 #'
 #' # we can now use `+` to add our object to a plot
 #' ggplot(mpg, aes(displ, cty)) +
@@ -109,97 +128,88 @@ add_ggplot <- function(p, object, objectname) {
 #'   element_text(colour = "red")
 #'
 #' # clean-up
-#' rm(ggplot_add.element_text)
-ggplot_add <- function(object, plot, object_name) {
-  UseMethod("ggplot_add")
-}
-#' @export
-ggplot_add.default <- function(object, plot, object_name) {
-  cli::cli_abort("Can't add {.var {object_name}} to a {.cls ggplot} object.")
-}
-#' @export
-ggplot_add.NULL <- function(object, plot, object_name) {
-  plot
-}
-#' @export
-ggplot_add.data.frame <- function(object, plot, object_name) {
-  plot$data <- object
-  plot
-}
-#' @export
-ggplot_add.function <- function(object, plot, object_name) {
-  cli::cli_abort(c(
-          "Can't add {.var {object_name}} to a {.cls ggplot} object",
-    "i" = "Did you forget to add parentheses, as in {.fn {object_name}}?"
-  ))
-}
-#' @export
-ggplot_add.theme <- function(object, plot, object_name) {
-  plot$theme <- add_theme(plot$theme, object)
-  plot
-}
-#' @export
-ggplot_add.Scale <- function(object, plot, object_name) {
-  plot$scales$add(object)
-  plot
-}
-#' @export
-ggplot_add.labels <- function(object, plot, object_name) {
-  update_labels(plot, object)
-}
-#' @export
-ggplot_add.Guides <- function(object, plot, object_name) {
-  if (is_guides(plot$guides)) {
-    # We clone the guides object to prevent modify-in-place of guides
-    old <- plot$guides
+ggplot_add <- S7::new_generic("ggplot_add", c("object", "plot"))
+
+S7::method(ggplot_add, list(S7::class_any, class_ggplot)) <-
+  function(object, plot, object_name, ...) {
+    cli::cli_abort("Can't add {.var {object_name}} to a {.cls ggplot} object.")
+  }
+
+S7::method(ggplot_add, list(S7::class_function, class_ggplot)) <-
+  function(object, plot, object_name, ...) {
+    cli::cli_abort(c(
+      "Can't add {.var {object_name}} to a {.cls ggplot} object",
+      "i" = "Did you forget to add parentheses, as in {.fn {object_name}}?"
+    ))
+  }
+
+S7::method(ggplot_add, list(NULL, class_ggplot)) <-
+  function(object, plot, ...) { plot }
+
+S7::method(ggplot_add, list(S7::class_data.frame, class_ggplot)) <-
+  function(object, plot, ...) { S7::set_props(plot, data = object) }
+
+S7::method(ggplot_add, list(class_scale, class_ggplot)) <-
+  function(object, plot, ...) {
+    plot@scales$add(object)
+    plot
+  }
+
+S7::method(ggplot_add, list(class_labels, class_ggplot)) <-
+  function(object, plot, ...) { update_labels(plot, object) }
+
+S7::method(ggplot_add, list(class_guides, class_ggplot)) <-
+  function(object, plot, ...) {
+    old <- plot@guides
     new <- ggproto(NULL, old)
     new$add(object)
-    plot$guides <- new
-  } else {
-    plot$guides <- object
+    plot@guides <- new
+    plot
   }
-  plot
-}
-#' @export
-ggplot_add.uneval <- function(object, plot, object_name) {
-  plot$mapping <- defaults(object, plot$mapping)
-  # defaults() doesn't copy class, so copy it.
-  class(plot$mapping) <- class(object)
-  plot
-}
-#' @export
-ggplot_add.Coord <- function(object, plot, object_name) {
-  if (!isTRUE(plot$coordinates$default)) {
-    cli::cli_inform("Coordinate system already present. Adding new coordinate system, which will replace the existing one.")
+
+S7::method(ggplot_add, list(class_mapping, class_ggplot)) <-
+  function(object, plot, ...) {
+    S7::set_props(plot, mapping = class_mapping(defaults(object, plot@mapping)))
   }
 
-  plot$coordinates <- object
-  plot
-}
-#' @export
-ggplot_add.Facet <- function(object, plot, object_name) {
-  plot$facet <- object
-  plot
-}
-#' @export
-ggplot_add.list <- function(object, plot, object_name) {
-  for (o in object) {
-    plot <- ggplot_add(o, plot, object_name)
+S7::method(ggplot_add, list(class_theme, class_ggplot)) <-
+  function(object, plot, ...) {
+    S7::set_props(plot, theme = add_theme(plot@theme, object))
   }
-  plot
-}
-#' @export
-ggplot_add.by <- function(object, plot, object_name) {
-  ggplot_add.list(object, plot, object_name)
-}
 
-#' @export
-ggplot_add.Layer <- function(object, plot, object_name) {
-  layers_names <- new_layer_names(object, names2(plot$layers))
-  plot$layers <- append(plot$layers, object)
-  names(plot$layers) <- layers_names
-  plot
-}
+S7::method(ggplot_add, list(class_coord, class_ggplot)) <-
+  function(object, plot, ...) {
+    if (!isTRUE(plot@coordinates$default)) {
+      cli::cli_inform(c(
+        "Coordinate system already present.",
+        i = "Adding new coordinate system, which will replace the existing one."
+      ))
+    }
+    S7::set_props(plot, coordinates = object)
+  }
+
+S7::method(ggplot_add, list(class_facet, class_ggplot)) <-
+  function(object, plot, ...) { S7::set_props(plot, facet = object) }
+
+S7::method(ggplot_add, list(class_layer, class_ggplot)) <-
+  function(object, plot, ...) {
+    layers_names <- new_layer_names(object, names2(plot@layers))
+    object <- setNames(append(plot@layers, object), layers_names)
+    S7::set_props(plot, layers = object)
+  }
+
+S7::method(ggplot_add, list(S7::class_list, class_ggplot)) <-
+  function(object, plot, object_name, ...) {
+    for (o in object) {
+      plot <- ggplot_add(o, plot, object_name)
+    }
+    plot
+  }
+
+S7::method(ggplot_add, list(S7::new_S3_class("by"), class_ggplot)) <-
+  function(object, plot, object_name, ...) {
+    ggplot_add(unclass(object), plot, object_name)
+  }
 
 new_layer_names <- function(layer, existing) {
 
diff --git a/R/plot.R b/R/plot.R
index 5f38f63116..d66e040d46 100644
--- a/R/plot.R
+++ b/R/plot.R
@@ -103,55 +103,53 @@
 #'     mapping = aes(x = group, y = group_mean), data = group_means_df,
 #'     colour = 'red', size = 3
 #'   )
-ggplot <- function(data = NULL, mapping = aes(), ...,
-                   environment = parent.frame()) {
-  UseMethod("ggplot")
-}
+ggplot <- S7::new_generic(
+  "ggplot2", "data",
+  fun = function(data, mapping = aes(), ..., environment = parent.frame()) {
+    force(mapping)
+    S7::S7_dispatch()
+  }
+)
 
-#' @export
-ggplot.default <- function(data = NULL, mapping = aes(), ...,
-                           environment = parent.frame()) {
+S7::method(ggplot, S7::class_any) <- function(
+    data, mapping = aes(), ...,
+    environment = parent.frame()) {
   if (!missing(mapping) && !is_mapping(mapping)) {
     cli::cli_abort(c(
       "{.arg mapping} must be created with {.fn aes}.",
       "x" = "You've supplied {.obj_type_friendly {mapping}}."
     ))
   }
+  if (missing(data)) {
+    data <- NULL
+  }
 
   data <- fortify(data, ...)
 
-  p <- structure(list(
+  p <- class_ggplot(
     data = data,
-    layers = list(),
-    scales = scales_list(),
-    guides = guides_list(),
     mapping = mapping,
-    theme = list(),
-    coordinates = coord_cartesian(default = TRUE),
-    facet = facet_null(),
-    plot_env = environment,
-    layout = ggproto(NULL, Layout),
-    labels = list()
-  ), class = c("gg", "ggplot"))
+    plot_env = environment
+  )
+  class(p) <- union("ggplot", class(p))
 
   set_last_plot(p)
   p
 }
 
-#' @export
-ggplot.function <- function(data = NULL, mapping = aes(), ...,
-                            environment = parent.frame()) {
-  # Added to avoid functions end in ggplot.default
-  cli::cli_abort(c(
-    "{.arg data} cannot be a function.",
-    "i" = "Have you misspelled the {.arg data} argument in {.fn ggplot}"
-  ))
-}
+S7::method(ggplot, S7::class_function) <-
+  function(data, mapping = aes(), ...,
+           environment = parent.frame()) {
+    # Added to avoid functions end in ggplot.default
+    cli::cli_abort(c(
+      "{.arg data} cannot be a function.",
+      "i" = "Have you misspelled the {.arg data} argument in {.fn ggplot}"
+    ))
+  }
 
 plot_clone <- function(plot) {
   p <- plot
-  p$scales <- plot$scales$clone()
-
+  p@scales <- plot@scales$clone()
   p
 }
 
@@ -160,7 +158,7 @@ plot_clone <- function(plot) {
 #' @keywords internal
 #' @export
 #' @name is_tests
-is_ggplot <- function(x) inherits(x, "ggplot")
+is_ggplot <- function(x) S7::S7_inherits(x, class_ggplot)
 
 #' @export
 #' @rdname is_tests
@@ -184,7 +182,9 @@ is.ggplot <- function(x) {
 #' @keywords hplot
 #' @return Invisibly returns the original plot.
 #' @export
-#' @method print ggplot
+#' @method print ggplot2::ggplot
+#' @name print.ggplot
+#' @aliases print.ggplot2::ggplot plot.ggplot2::ggplot
 #' @examples
 #' colours <- c("class", "drv", "fl")
 #'
@@ -198,7 +198,8 @@ is.ggplot <- function(x) {
 #'   print(ggplot(mpg, aes(displ, hwy, colour = .data[[colour]])) +
 #'           geom_point())
 #' }
-print.ggplot <- function(x, newpage = is.null(vp), vp = NULL, ...) {
+# TODO: should convert to proper S7 method once bug in S7 is resolved
+`print.ggplot2::ggplot` <- function(x, newpage = is.null(vp), vp = NULL, ...) {
   set_last_plot(x)
   if (newpage) grid.newpage()
 
@@ -227,7 +228,44 @@ print.ggplot <- function(x, newpage = is.null(vp), vp = NULL, ...) {
 
   invisible(x)
 }
-#' @rdname print.ggplot
-#' @method plot ggplot
+
+S7::method(plot, class_ggplot) <- `print.ggplot2::ggplot`
+
+# The following extractors and subassignment operators are for a smooth
+# transition and should be deprecated in the release cycle after 4.0.0
+# TODO: should convert to proper S7 method once bug in S7 is resolved
+
+#' @export
+`$.ggplot2::gg` <- function(x, i) {
+  `[[`(S7::props(x), i)
+}
+
+#' @export
+`$<-.ggplot2::gg` <- function(x, i, value) {
+  S7::props(x) <- `$<-`(S7::props(x), i, value)
+  x
+}
+
+#' @export
+`[.ggplot2::gg` <- function(x, i) {
+  `[`(S7::props(x), i)
+}
+
+#' @export
+`[<-.ggplot2::gg` <- function(x, i, value) {
+  S7::props(x) <- `[<-`(S7::props(x), i, value)
+  x
+}
+
+#' @export
+`[[.ggplot2::gg` <- function(x, i) {
+  `[[`(S7::props(x), i)
+}
+
 #' @export
-plot.ggplot <- print.ggplot
+`[[<-.ggplot2::gg` <- function(x, i, value) {
+  S7::props(x) <- `[[<-`(S7::props(x), i, value)
+  x
+}
+
+
diff --git a/R/properties.R b/R/properties.R
new file mode 100644
index 0000000000..493d787f05
--- /dev/null
+++ b/R/properties.R
@@ -0,0 +1,45 @@
+property_boolean <- function(allow_null = FALSE, default = TRUE) {
+  class <- S7::class_logical
+  class <- if (allow_null) S7::new_union(class, NULL) else class
+  validator <- function(value) {
+    if ((allow_null && is.null(value)) || is_bool(value)) {
+      return(character())
+    }
+    "must be a boolean"
+  }
+  S7::new_property(
+    class = class,
+    validator = validator,
+    default = default
+  )
+}
+
+property_choice <- function(options, allow_null = FALSE, default = NULL) {
+  force(options)
+  class <- S7::class_character
+  class <- if (allow_null) S7::new_union(class, NULL) else class
+  validator <- function(value) {
+    if (allow_null && is.null(value)) {
+      return(character())
+    }
+    if (!is_string(value)) {
+      return(as_cli("must be a string, not {.obj_type_friendly {value}}"))
+    }
+    if (value %in% options) {
+      return(character())
+    }
+    as_cli("must be one of {.or {.val {options}}}")
+  }
+  S7::new_property(
+    class = class,
+    validator = validator,
+    default = default
+  )
+}
+
+property_nullable <- function(class = S7::class_any, ...) {
+  S7::new_property(
+    class = S7::new_union(NULL, class),
+    ...
+  )
+}
diff --git a/R/quick-plot.R b/R/quick-plot.R
index 64e2ab460d..bac170ce43 100644
--- a/R/quick-plot.R
+++ b/R/quick-plot.R
@@ -78,7 +78,7 @@ qplot <- function(x, y, ..., data, facets = NULL, margins = FALSE,
   is_constant <- (!names(exprs) %in% ggplot_global$all_aesthetics) |
     vapply(exprs, quo_is_call, logical(1), name = "I")
 
-  mapping <- new_aes(exprs[!is_missing & !is_constant], env = parent.frame())
+  mapping <- class_mapping(exprs[!is_missing & !is_constant], env = parent.frame())
 
   consts <- exprs[is_constant]
 
diff --git a/R/save.R b/R/save.R
index 2f2faec357..b4b1cc7226 100644
--- a/R/save.R
+++ b/R/save.R
@@ -244,7 +244,8 @@ get_plot_background <- function(plot, bg = NULL, default = "transparent") {
   if (!is_ggplot(plot)) {
     return(default)
   }
-  calc_element("plot.background", plot_theme(plot))$fill %||% default
+  bg <- calc_element("plot.background", plot_theme(plot))
+  try_prop(bg, "fill") %||% "transparent"
 }
 
 validate_device <- function(device, filename = NULL, dpi = 300, call = caller_env()) {
@@ -325,10 +326,7 @@ validate_device <- function(device, filename = NULL, dpi = 300, call = caller_en
   dev
 }
 
-#' @export
-grid.draw.ggplot <- function(x, recording = TRUE) {
-  print(x)
-}
+S7::method(grid.draw, class_ggplot) <- function(x, recording = TRUE) print(x)
 
 absorb_grdevice_args <- function(f) {
   function(..., type, antialias) {
diff --git a/R/summarise-plot.R b/R/summarise-plot.R
index 9ab046cb8c..39d3df5c17 100644
--- a/R/summarise-plot.R
+++ b/R/summarise-plot.R
@@ -62,8 +62,8 @@ NULL
 #' @rdname summarise_plot
 #' @export
 summarise_layout <- function(p) {
-  check_inherits(p, "ggplot_built")
-  l <- p$layout
+  check_inherits(p, "ggplot2::ggplot_built")
+  l <- p@layout
 
   layout <- l$layout
   layout <- data_frame0(
@@ -99,7 +99,7 @@ summarise_layout <- function(p) {
 #' @rdname summarise_plot
 #' @export
 summarise_coord <- function(p) {
-  check_inherits(p, "ggplot_built")
+  check_inherits(p, "ggplot2::ggplot_built")
 
   # Given a transform object, find the log base; if the transform object is
   # NULL, or if it's not a log transform, return NA.
@@ -112,9 +112,9 @@ summarise_coord <- function(p) {
   }
 
   list(
-    xlog = trans_get_log_base(p$layout$coord$trans$x),
-    ylog = trans_get_log_base(p$layout$coord$trans$y),
-    flip = inherits(p$layout$coord, "CoordFlip")
+    xlog = trans_get_log_base(p@layout$coord$trans$x),
+    ylog = trans_get_log_base(p@layout$coord$trans$y),
+    flip = inherits(p@layout$coord, "CoordFlip")
   )
 }
 
@@ -122,13 +122,13 @@ summarise_coord <- function(p) {
 #' @rdname summarise_plot
 #' @export
 summarise_layers <- function(p) {
-  check_inherits(p, "ggplot_built")
+  check_inherits(p, "ggplot2::ggplot_built")
 
-  # Default mappings. Make sure it's a regular list instead of an uneval
+  # Default mappings. Make sure it's a regular list instead of a mapping
   # object.
-  default_mapping <- unclass(p$plot$mapping)
+  default_mapping <- unclass(p@plot@mapping)
 
-  layer_mappings <- lapply(p$plot$layers, function(layer) {
+  layer_mappings <- lapply(p@plot@layers, function(layer) {
     defaults(layer$mapping, default_mapping)
   })
 
diff --git a/R/summary.R b/R/summary.R
index 4a227a3599..8c3d252906 100644
--- a/R/summary.R
+++ b/R/summary.R
@@ -1,41 +1,43 @@
 #' Displays a useful description of a ggplot object
 #'
+#' @noRd
 #' @param object ggplot2 object to summarise
 #' @param ... other arguments ignored (for compatibility with generic)
 #' @keywords internal
-#' @method summary ggplot
-#' @export
+#' @name summary.ggplot
+#' @aliases summary.ggplot summary.ggplot2::ggplot
+#' @usage summary(object, ...)
 #' @examples
 #' p <- ggplot(mtcars, aes(mpg, wt)) +
 #'   geom_point()
 #' summary(p)
-summary.ggplot <- function(object, ...) {
+S7::method(summary, class_ggplot) <- function(object, ...) {
   wrap <- function(x) paste(
     paste(strwrap(x, exdent = 2), collapse = "\n"),
     "\n", sep = ""
     )
 
-  if (!is.null(object$data)) {
+  if (!is.null(object@data)) {
     output <- paste(
-      "data:     ", paste(names(object$data), collapse = ", "),
-      " [", nrow(object$data), "x", ncol(object$data), "] ",
+      "data:     ", paste(names(object@data), collapse = ", "),
+      " [", nrow(object@data), "x", ncol(object@data), "] ",
       "\n", sep = "")
     cat(wrap(output))
   }
-  if (length(object$mapping) > 0) {
-    cat("mapping:  ", clist(object$mapping), "\n", sep = "")
+  if (length(object@mapping) > 0) {
+    cat("mapping:  ", clist(object@mapping), "\n", sep = "")
   }
-  if (object$scales$n() > 0) {
-    cat("scales:  ", paste(object$scales$input(), collapse = ", "), "\n")
+  if (object@scales$n() > 0) {
+    cat("scales:  ", paste(object@scales$input(), collapse = ", "), "\n")
   }
 
-  vars <- object$facet$vars()
+  vars <- object@facet$vars()
   vars <- if (length(vars) > 0) paste0("~", vars) else "<empty>"
   cat("faceting: ", paste0(vars, collapse = ", "), "\n")
 
-  if (length(object$layers) > 0)
+  if (length(object@layers) > 0)
     cat("-----------------------------------\n")
-  invisible(lapply(object$layers, function(x) {
+  invisible(lapply(object@layers, function(x) {
     print(x)
     cat("\n")
   }))
diff --git a/R/theme-current.R b/R/theme-current.R
index c6848c7d76..e42f8c1e68 100644
--- a/R/theme-current.R
+++ b/R/theme-current.R
@@ -40,7 +40,7 @@ NULL
 #' @return `set_theme()`, `update_theme()`, and `replace_theme()`
 #'   invisibly return the previous theme so you can easily save it, then
 #'   later restore it.
-#' @seealso [+.gg()]
+#' @seealso [add_gg()]
 #' @export
 #' @examples
 #' p <- ggplot(mtcars, aes(mpg, wt)) +
diff --git a/R/theme-defaults.R b/R/theme-defaults.R
index 7b5bb286f7..3823bf45c3 100644
--- a/R/theme-defaults.R
+++ b/R/theme-defaults.R
@@ -127,11 +127,12 @@ theme_grey <- function(base_size = 11, base_family = "",
     # by others
     line =               element_line(
                            colour = ink, linewidth = base_line_size,
-                           linetype = 1, lineend = "butt"
+                           linetype = 1, lineend = "butt", linejoin = "round"
                          ),
     rect =               element_rect(
                            fill = paper, colour = ink,
-                           linewidth = base_rect_size, linetype = 1
+                           linewidth = base_rect_size, linetype = 1,
+                           linejoin = "round"
                          ),
     text =               element_text(
                             family = base_family, face = "plain",
@@ -153,7 +154,7 @@ theme_grey <- function(base_size = 11, base_family = "",
 
     polygon =            element_polygon(
                            fill = paper, colour = ink,
-                           linewidth = base_rect_size, linetype = 1
+                           linewidth = base_rect_size, linetype = 1, linejoin = "round"
                          ),
 
     geom =               element_geom(
@@ -525,7 +526,7 @@ theme_void <- function(base_size = 11, base_family = "",
     line =               element_blank(),
     rect =               element_rect(
                            fill = paper, colour = NA, linewidth = 0, linetype = 1,
-                           inherit.blank = FALSE
+                           inherit.blank = FALSE, linejoin = "round"
                          ),
     polygon =            element_blank(),
     point =              element_blank(),
@@ -614,11 +615,11 @@ theme_test <- function(base_size = 11, base_family = "",
   t <- theme(
     line =               element_line(
                            colour = ink, linewidth = base_line_size,
-                           linetype = 1, lineend = "butt"
+                           linetype = 1, lineend = "butt", linejoin = "round"
                          ),
     rect =               element_rect(
                            fill = paper, colour = ink,
-                           linewidth = base_rect_size, linetype = 1
+                           linewidth = base_rect_size, linetype = 1, linejoin = "round"
                          ),
     text =               element_text(
                             family = base_family, face = "plain",
@@ -633,7 +634,7 @@ theme_test <- function(base_size = 11, base_family = "",
                          ),
     polygon =            element_polygon(
                            fill = paper, colour = ink,
-                           linewidth = base_rect_size, linetype = 1
+                           linewidth = base_rect_size, linetype = 1, linejoin = "round"
                          ),
     title =              element_text(family = header_family),
     spacing = unit(half_line, "pt"),
diff --git a/R/theme-elements.R b/R/theme-elements.R
index a16302b6db..0698bb12dd 100644
--- a/R/theme-elements.R
+++ b/R/theme-elements.R
@@ -81,55 +81,93 @@ NULL
 
 #' @export
 #' @rdname element
-element_blank <- function() {
-  structure(
-    list(),
-    class = c("element_blank", "element")
-  )
-}
+element <- S7::new_class("element", abstract = TRUE)
 
 #' @export
 #' @rdname element
-element_rect <- function(fill = NULL, colour = NULL, linewidth = NULL,
-  linetype = NULL, color = NULL, inherit.blank = FALSE, size = deprecated()) {
+element_blank <- S7::new_class("element_blank", parent = element)
+
+# All properties are listed here so they can easily be recycled in the different
+# element classes
+#' @include properties.R
+#' @include margins.R
+element_props <- list(
+  fill       = property_nullable(S7::class_character | S7::new_S3_class("GridPattern") | S7::class_logical),
+  colour     = property_nullable(S7::class_character | S7::class_logical),
+  family     = property_nullable(S7::class_character),
+  hjust      = property_nullable(S7::class_numeric),
+  vjust      = property_nullable(S7::class_numeric),
+  angle      = property_nullable(S7::class_numeric),
+  size       = property_nullable(S7::class_numeric),
+  lineheight = property_nullable(S7::class_numeric),
+  margin     = property_nullable(margin),
+  face       = property_choice(c("plain", "bold", "italic", "oblique", "bold.italic"), allow_null = TRUE),
+  linewidth  = property_nullable(S7::class_numeric),
+  linetype   = property_nullable(S7::class_numeric | S7::class_character),
+  lineend    = property_choice(c("round", "butt", "square"), allow_null = TRUE),
+  linejoin   = property_choice(c("round", "mitre", "bevel"), allow_null = TRUE),
+  shape      = property_nullable(S7::class_numeric | S7::class_character),
+  arrow      = property_nullable(S7::new_S3_class("arrow") | S7::class_logical),
+  arrow.fill = property_nullable(S7::class_character | S7::class_logical),
+  debug      = property_boolean(allow_null = TRUE, default = NULL),
+  inherit.blank = property_boolean(default = FALSE)
+)
 
-  if (lifecycle::is_present(size)) {
-    deprecate_warn0("3.4.0", "element_rect(size)", "element_rect(linewidth)")
-    linewidth <- size
+#' @export
+#' @rdname element
+element_rect <- S7::new_class(
+  "element_rect", parent = element,
+  properties = element_props[c("fill", "colour",
+                               "linewidth", "linetype", "linejoin",
+                               "inherit.blank")],
+  constructor = function(fill = NULL, colour = NULL, linewidth = NULL,
+                         linetype = NULL, color = NULL, linejoin = NULL,
+                         inherit.blank = FALSE, size = deprecated()){
+    if (lifecycle::is_present(size)) {
+      deprecate_warn0("3.4.0", "element_rect(size)", "element_rect(linewidth)")
+      linewidth <- size
+    }
+    S7::new_object(
+      S7::S7_object(),
+      fill = fill, colour = color %||% colour,
+      linewidth = linewidth, linetype = linetype, linejoin = linejoin,
+      inherit.blank = inherit.blank
+    )
   }
-
-  if (!is.null(color))  colour <- color
-  structure(
-    list(fill = fill, colour = colour, linewidth = linewidth, linetype = linetype,
-         inherit.blank = inherit.blank),
-    class = c("element_rect", "element")
-  )
-}
+)
 
 #' @export
 #' @rdname element
-#' @param lineend Line end Line end style (round, butt, square)
+#' @param linejoin Line join style, one of `"round"`, `"mitre"` or `"bevel"`.
+#' @param lineend Line end style, one of `"round"`, `"butt"` or `"square"`.
 #' @param arrow Arrow specification, as created by [grid::arrow()]
-element_line <- function(colour = NULL, linewidth = NULL, linetype = NULL,
-  lineend = NULL, color = NULL, arrow = NULL, arrow.fill = NULL,
-  inherit.blank = FALSE, size = deprecated()) {
-
-  if (lifecycle::is_present(size)) {
-    deprecate_warn0("3.4.0", "element_line(size)", "element_line(linewidth)")
-    linewidth <- size
+element_line <- S7::new_class(
+  "element_line", parent = element,
+  properties = element_props[c(
+    "colour", "linewidth", "linetype", "lineend", "linejoin",
+    "arrow", "arrow.fill",
+    "inherit.blank"
+  )],
+  constructor = function(colour = NULL, linewidth = NULL, linetype = NULL,
+                         lineend = NULL, color = NULL, linejoin = NULL,
+                         arrow = NULL, arrow.fill = NULL,
+                         inherit.blank = FALSE, size = deprecated()) {
+    if (lifecycle::is_present(size)) {
+      deprecate_warn0("3.4.0", "element_line(size)", "element_line(linewidth)")
+      linewidth <- size
+    }
+    colour <- color %||% colour
+    S7::new_object(
+      S7::S7_object(),
+      colour = colour,
+      linewidth = linewidth, linetype = linetype, lineend = lineend,
+      linejoin = linejoin,
+      arrow = arrow %||% FALSE,
+      arrow.fill = arrow.fill %||% colour,
+      inherit.blank = inherit.blank
+    )
   }
-
-  colour <- color %||% colour
-  arrow.fill <- arrow.fill %||% colour
-  arrow <- arrow %||% FALSE
-
-  structure(
-    list(colour = colour, linewidth = linewidth, linetype = linetype, lineend = lineend,
-      arrow = arrow, arrow.fill = arrow.fill, inherit.blank = inherit.blank),
-    class = c("element_line", "element")
-  )
-}
-
+)
 
 #' @param family Font family
 #' @param face Font face ("plain", "italic", "bold", "bold.italic")
@@ -145,116 +183,121 @@ element_line <- function(colour = NULL, linewidth = NULL, linetype = NULL,
 #'   is anchored.
 #' @export
 #' @rdname element
-element_text <- function(family = NULL, face = NULL, colour = NULL,
-  size = NULL, hjust = NULL, vjust = NULL, angle = NULL, lineheight = NULL,
-  color = NULL, margin = NULL, debug = NULL, inherit.blank = FALSE) {
-
-  if (!is.null(color))  colour <- color
-
-  n <- max(
-    length(family), length(face), length(colour), length(size),
-    length(hjust), length(vjust), length(angle), length(lineheight)
-  )
-  if (n > 1) {
-    cli::cli_warn(c(
-      "Vectorized input to {.fn element_text} is not officially supported.",
-      "i" = "Results may be unexpected or may change in future versions of ggplot2."
-    ))
-  }
-
-
-  structure(
-    list(family = family, face = face, colour = colour, size = size,
+element_text <- S7::new_class(
+  "element_text", parent = element,
+  properties = element_props[c(
+    "family", "face", "colour", "size", "hjust", "vjust", "angle", "lineheight",
+    "margin", "debug", "inherit.blank"
+  )],
+  constructor = function(family = NULL, face = NULL, colour = NULL,
+                         size = NULL, hjust = NULL, vjust = NULL, angle = NULL,
+                         lineheight = NULL, color = NULL, margin = NULL,
+                         debug = NULL, inherit.blank = FALSE) {
+    n <- max(
+      length(family), length(face), length(colour), length(size),
+      length(hjust), length(vjust), length(angle), length(lineheight)
+    )
+    if (n > 1) {
+      cli::cli_warn(c(
+        "Vectorized input to {.fn element_text} is not officially supported.",
+        "i" = "Results may be unexpected or may change in future versions of ggplot2."
+      ))
+    }
+
+    colour <- color %||% colour
+    S7::new_object(
+      S7::S7_object(),
+      family = family, face = face, colour = colour, size = size,
       hjust = hjust, vjust = vjust, angle = angle, lineheight = lineheight,
-      margin = margin, debug = debug, inherit.blank = inherit.blank),
-    class = c("element_text", "element")
-  )
-}
-
-#' @export
-#' @param type For testing elements: the type of element to expect. One of
-#'   `"blank"`, `"rect"`, `"line"` or `"text"`.
-#' @rdname is_tests
-is_theme_element <- function(x, type = "any") {
-  switch(
-    type %||% "any",
-    any   = inherits(x, "element"),
-    rect  = inherits(x, "element_rect"),
-    line  = inherits(x, "element_line"),
-    text  = inherits(x, "element_text"),
-    blank = inherits(x, "element_blank"),
-    # TODO: ideally we accept more elements from extensions. We need to
-    # consider how this will work with S7 classes, where ggplot2 doesn't know
-    # about the extension's class objects.
-    FALSE
-  )
-}
+      margin = margin, debug = debug, inherit.blank = inherit.blank
+    )
+  }
+)
 
 #' @export
 #' @rdname element
-element_polygon <- function(fill = NULL, colour = NULL, linewidth = NULL,
-                            linetype = NULL, color = NULL,
-                            inherit.blank = FALSE) {
-  structure(
-    list(
+element_polygon <- S7::new_class(
+  "element_polygon", parent = element,
+  properties = element_props[c(
+    "fill", "colour", "linewidth", "linetype", "linejoin", "inherit.blank"
+  )],
+  constructor = function(fill = NULL, colour = NULL, linewidth = NULL,
+                         linetype = NULL, color = NULL, linejoin = NULL,
+                         inherit.blank = FALSE) {
+    colour <- color %||% colour
+    S7::new_object(
+      S7::S7_object(),
       fill = fill, colour = color %||% colour, linewidth = linewidth,
-      linetype = linetype, inherit.blank = inherit.blank
-    ),
-    class = c("element_polygon", "element")
-  )
-}
+      linetype = linetype, linejoin = linejoin, inherit.blank = inherit.blank
+    )
+  }
+)
 
 #' @export
 #' @rdname element
-element_point <- function(colour = NULL, shape = NULL, size = NULL, fill = NULL,
-                          stroke = NULL, color = NULL, inherit.blank = FALSE) {
-  structure(
-    list(
+element_point <- S7::new_class(
+  "element_point", parent = element,
+  properties = rename(
+    element_props[c(
+      "colour", "shape", "size", "fill", "linewidth", "inherit.blank"
+    )],
+    c("linewidth" = "stroke")
+  ),
+  constructor = function(colour = NULL, shape = NULL, size = NULL, fill = NULL,
+                         stroke = NULL, color = NULL, inherit.blank = FALSE) {
+    S7::new_object(
+      S7::S7_object(),
       colour = color %||% colour, fill = fill, shape = shape, size = size,
       stroke = stroke, inherit.blank = inherit.blank
-    ),
-    class = c("element_point", "element")
-  )
-}
+    )
+  }
+)
 
 #' @param ink Foreground colour.
 #' @param paper Background colour.
 #' @param accent Accent colour.
 #' @export
 #' @rdname element
-element_geom <- function(
-    # colours
-  ink = NULL, paper = NULL, accent = NULL,
-  # linewidth
-  linewidth = NULL, borderwidth = NULL,
-  # linetype
-  linetype = NULL, bordertype = NULL,
-  # text
-  family = NULL, fontsize = NULL,
-  # points
-  pointsize = NULL, pointshape = NULL,
-
-  colour = NULL, color = NULL, fill = NULL) {
-
-  if (!is.null(fontsize)) {
-    fontsize <- fontsize / .pt
-  }
-
-  structure(
-    list(
-      ink = ink,
-      paper = paper,
-      accent = accent,
+element_geom <- S7::new_class(
+  "element_geom", parent = element,
+  properties = list(
+    ink = element_props$colour,
+    paper = element_props$colour,
+    accent = element_props$colour,
+    linewidth = element_props$linewidth,
+    borderwidth = element_props$linewidth,
+    linetype = element_props$linetype,
+    bordertype = element_props$linetype,
+    family = element_props$family,
+    fontsize = element_props$size,
+    pointsize = element_props$size,
+    pointshape = element_props$shape,
+    colour = element_props$colour,
+    fill = element_props$fill
+  ),
+  constructor = function(
+    ink = NULL, paper = NULL, accent = NULL,
+    linewidth = NULL, borderwidth = NULL,
+    linetype = NULL, bordertype = NULL,
+    family = NULL, fontsize = NULL,
+    pointsize = NULL, pointshape = NULL,
+    colour = NULL, color = NULL, fill = NULL) {
+
+    if (!is.null(fontsize)) {
+      fontsize <- fontsize / .pt
+    }
+
+    S7::new_object(
+      S7::S7_object(),
+      ink = ink, paper = paper, accent = accent,
       linewidth = linewidth, borderwidth = borderwidth,
       linetype = linetype, bordertype = bordertype,
       family = family, fontsize = fontsize,
       pointsize = pointsize, pointshape = pointshape,
-      colour = color %||% colour,
-      fill = fill
-    ),
-    class = c("element_geom", "element")
-  )
-}
+      colour = color %||% colour, fill = fill
+    )
+  }
+)
 
 .default_geom_element <- element_geom(
   ink = "black", paper = "white", accent = "#3366FF",
@@ -268,6 +311,24 @@ element_geom <- function(
 #' @export
 print.element <- function(x, ...) utils::str(x)
 
+#' @export
+#' @param type For testing elements: the type of element to expect. One of
+#'   `"blank"`, `"rect"`, `"line"`, `"text"`, `"polygon"`, `"point"` or `"geom"`.
+#' @rdname is_tests
+is_theme_element <- function(x, type = "any") {
+  switch(
+    type %||% "any",
+    any     = S7::S7_inherits(x, element),
+    blank   = S7::S7_inherits(x, element_blank),
+    rect    = S7::S7_inherits(x, element_rect),
+    line    = S7::S7_inherits(x, element_line),
+    text    = S7::S7_inherits(x, element_text),
+    polygon = S7::S7_inherits(x, element_polygon),
+    point   = S7::S7_inherits(x, element_point),
+    geom    = S7::S7_inherits(x, element_geom),
+    FALSE
+  )
+}
 
 #' @param x A single number specifying size relative to parent element.
 #' @rdname element
@@ -276,6 +337,45 @@ rel <- function(x) {
   structure(x, class = "rel")
 }
 
+#' @export
+`$.ggplot2::element` <- function(x, i) {
+  # deprecate_soft0("4.1.0", I("`<ggplot2::element>$i`"), I("`<ggplot2::element>@i`"))
+  `[[`(S7::props(x), i)
+}
+
+#' @export
+`[.ggplot2::element` <- function(x, i) {
+  # deprecate_soft0("4.1.0", I("`<gglot2::element>[i]`"), I("`S7::props(<ggplot2::element>, i)`"))
+  `[`(S7::props(x), i)
+}
+
+#' @export
+`[[.ggplot2::element` <- function(x, i) {
+  # deprecate_soft0("4.1.0", I("`<ggplot2::element>[[i]]`"), I("`S7::prop(<ggplot2::element>, i)`"))
+  `[[`(S7::props(x), i)
+}
+
+#' @export
+`$<-.ggplot2::element` <- function(x, i, value) {
+  # deprecate_soft0("4.1.0", I("`<ggplot2::element>$i <- value`"), I("`<ggplot2::element>@i <- value`"))
+  S7::props(x) <- `[[<-`(S7::props(x), i, value)
+  x
+}
+
+#' @export
+`[<-.ggplot2::element` <- function(x, i, value) {
+  # deprecate_soft0("4.1.0", I("`<ggplot2::element>[i] <- value`"), I("`S7::props(<ggplot2::element>)[i] <- value`"))
+  S7::props(x) <- `[<-`(S7::props(x), i, value)
+  x
+}
+
+#' @export
+`[[<-.ggplot2::element` <- function(x, i, value) {
+  # deprecate_soft0("4.1.0", I("`<ggplot2::element>[[i]] <- value`"), I("S7::prop(<ggplot2::element>, i) <- value"))
+  S7::props(x) <- `[[<-`(S7::props(x), i, value)
+  x
+}
+
 #' @export
 print.rel <- function(x, ...) print(noquote(paste(x, " *", sep = "")))
 
@@ -314,134 +414,131 @@ element_render <- function(theme, element, ..., name = NULL) {
 #'   usually at least position. See the source code for individual methods.
 #' @keywords internal
 #' @export
-element_grob <- function(element, ...) {
-  UseMethod("element_grob")
-}
-
-#' @export
-element_grob.element_blank <- function(element, ...)  zeroGrob()
-
-#' @export
-element_grob.element_rect <- function(element, x = 0.5, y = 0.5,
-  width = 1, height = 1,
-  fill = NULL, colour = NULL, linewidth = NULL, linetype = NULL, ..., size = deprecated()) {
+element_grob <- S7::new_generic("element_grob", "element")
 
-  if (lifecycle::is_present(size)) {
-    deprecate_warn0("3.4.0", "element_grob.element_rect(size)", "element_grob.element_rect(linewidth)")
-    linewidth <- size
-  }
+S7::method(element_grob, element_blank) <- function(element, ...) zeroGrob()
 
-  # The gp settings can override element_gp
-  gp <- gg_par(lwd = linewidth, col = colour, fill = fill, lty = linetype)
-  element_gp <- gg_par(lwd = element$linewidth, col = element$colour,
-    fill = element$fill, lty = element$linetype)
+S7::method(element_grob, element_rect) <-
+  function(element, x = 0.5, y = 0.5, width = 1, height = 1,
+           fill = NULL, colour = NULL,
+           linewidth = NULL, linetype = NULL, linejoin = NULL,
+           ..., size = deprecated()) {
 
-  rectGrob(x, y, width, height, gp = modify_list(element_gp, gp), ...)
-}
+    if (lifecycle::is_present(size)) {
+      deprecate_warn0("3.4.0", "element_grob.element_rect(size)", "element_grob.element_rect(linewidth)")
+      linewidth <- size
+    }
 
+    gp <- gg_par(lwd = linewidth, col = colour, fill = fill, lty = linetype, linejoin = linejoin)
+    element_gp <- gg_par(lwd = element@linewidth, col = element@colour,
+                         fill = element@fill, lty = element@linetype,
+                         linejoin = element@linejoin)
 
-#' @export
-element_grob.element_text <- function(element, label = "", x = NULL, y = NULL,
-  family = NULL, face = NULL, colour = NULL, size = NULL,
-  hjust = NULL, vjust = NULL, angle = NULL, lineheight = NULL,
-  margin = NULL, margin_x = FALSE, margin_y = FALSE, ...) {
+    rectGrob(x, y, width, height, gp = modify_list(element_gp, gp), ...)
+  }
 
-  if (is.null(label))
-    return(zeroGrob())
+S7::method(element_grob, element_text) <-
+  function(element, label = "", x = NULL, y = NULL,
+           family = NULL, face = NULL, colour = NULL, size = NULL,
+           hjust = NULL, vjust = NULL, angle = NULL, lineheight = NULL,
+           margin = NULL, margin_x = FALSE, margin_y = FALSE, ...) {
 
-  vj <- vjust %||% element$vjust
-  hj <- hjust %||% element$hjust
-  margin <- margin %||% element$margin
+    if (is.null(label))
+      return(zeroGrob())
 
-  angle <- angle %||% element$angle %||% 0
+    vj <- vjust %||% element@vjust
+    hj <- hjust %||% element@hjust
+    margin <- margin %||% element@margin
 
-  # The gp settings can override element_gp
-  gp <- gg_par(fontsize = size, col = colour,
-    fontfamily = family, fontface = face,
-    lineheight = lineheight)
-  element_gp <- gg_par(fontsize = element$size, col = element$colour,
-    fontfamily = element$family, fontface = element$face,
-    lineheight = element$lineheight)
+    angle <- angle %||% element@angle %||% 0
 
-  titleGrob(label, x, y, hjust = hj, vjust = vj, angle = angle,
-    gp = modify_list(element_gp, gp), margin = margin,
-    margin_x = margin_x, margin_y = margin_y, debug = element$debug, ...)
-}
+    # The gp settings can override element_gp
+    gp <- gg_par(fontsize = size, col = colour,
+                 fontfamily = family, fontface = face,
+                 lineheight = lineheight)
+    element_gp <- gg_par(fontsize = element@size, col = element@colour,
+                         fontfamily = element@family, fontface = element@face,
+                         lineheight = element@lineheight)
 
+    titleGrob(label, x, y, hjust = hj, vjust = vj, angle = angle,
+              gp = modify_list(element_gp, gp), margin = margin,
+              margin_x = margin_x, margin_y = margin_y, debug = element@debug, ...)
+  }
 
+S7::method(element_grob, element_line) <-
+  function(element, x = 0:1, y = 0:1,
+           colour = NULL, linewidth = NULL, linetype = NULL, lineend = NULL,
+           linejoin = NULL, arrow.fill = NULL,
+           default.units = "npc", id.lengths = NULL, ..., size = deprecated()) {
+
+    if (lifecycle::is_present(size)) {
+      deprecate_warn0("3.4.0", "element_grob.element_line(size)", "element_grob.element_line(linewidth)")
+      linewidth <- size
+    }
+
+    arrow <- if (is.logical(element@arrow) && !element@arrow) {
+      NULL
+    } else {
+      element@arrow
+    }
+    if (is.null(arrow)) {
+      arrow.fill <- colour
+      element@arrow.fill <- element@colour
+    }
+
+    # The gp settings can override element_gp
+    gp <- gg_par(
+      col = colour, fill = arrow.fill %||% colour,
+      lwd = linewidth, lty = linetype, lineend = lineend, linejoin = linejoin
+    )
+    element_gp <- gg_par(
+      col = element@colour, fill = element@arrow.fill %||% element@colour,
+      lwd = element@linewidth, lty = element@linetype,
+      lineend = element@lineend, linejoin = element@linejoin
+    )
 
-#' @export
-element_grob.element_line <- function(element, x = 0:1, y = 0:1,
-  colour = NULL, linewidth = NULL, linetype = NULL, lineend = NULL,
-  arrow.fill = NULL,
-  default.units = "npc", id.lengths = NULL, ..., size = deprecated()) {
-
-  if (lifecycle::is_present(size)) {
-    deprecate_warn0("3.4.0", "element_grob.element_line(size)", "element_grob.element_line(linewidth)")
-    linewidth <- size
+    polylineGrob(
+      x, y, default.units = default.units,
+      gp = modify_list(element_gp, gp),
+      id.lengths = id.lengths, arrow = arrow, ...
+    )
   }
 
-  arrow <- if (is.logical(element$arrow) && !element$arrow) {
-    NULL
-  } else {
-    element$arrow
-  }
-  if (is.null(arrow)) {
-    arrow.fill <- colour
-    element$arrow.fill <- element$colour
+S7::method(element_grob, element_polygon) <-
+  function(element, x = c(0, 0.5, 1, 0.5),
+           y = c(0.5, 1, 0.5, 0), fill = NULL,
+           colour = NULL, linewidth = NULL,
+           linetype = NULL, linejoin = NULL, ...,
+           id = NULL, id.lengths = NULL,
+           pathId = NULL, pathId.lengths = NULL) {
+
+    gp <- gg_par(lwd = linewidth, col = colour, fill = fill,
+                 lty = linetype, linejoin = linejoin)
+    element_gp <- gg_par(lwd = element@linewidth, col = element@colour,
+                         fill = element@fill, lty = element@linetype,
+                         linejoin = element@linejoin)
+    pathGrob(
+      x = x, y = y, gp = modify_list(element_gp, gp), ...,
+      # We swap the id logic so that `id` is always the (super)group id
+      # (consistent with `polygonGrob()`) and `pathId` always the subgroup id.
+      pathId = id, pathId.lengths = id.lengths,
+      id = pathId, id.lengths = pathId.lengths
+    )
   }
 
-  # The gp settings can override element_gp
-  gp <- gg_par(
-    col = colour, fill = arrow.fill %||% colour,
-    lwd = linewidth, lty = linetype, lineend = lineend
-  )
-  element_gp <- gg_par(
-    col = element$colour, fill = element$arrow.fill %||% element$colour,
-    lwd = element$linewidth, lty = element$linetype,
-    lineend = element$lineend
-  )
-
-  polylineGrob(
-    x, y, default.units = default.units,
-    gp = modify_list(element_gp, gp),
-    id.lengths = id.lengths, arrow = arrow, ...
-  )
-}
-
-#' @export
-element_grob.element_polygon <- function(element, x = c(0, 0.5, 1, 0.5),
-                                         y = c(0.5, 1, 0.5, 0), fill = NULL,
-                                         colour = NULL, linewidth = NULL,
-                                         linetype = NULL, ...,
-                                         id = NULL, id.lengths = NULL,
-                                         pathId = NULL, pathId.lengths = NULL) {
-
-  gp <- gg_par(lwd = linewidth, col = colour, fill = fill, lty = linetype)
-  element_gp <- gg_par(lwd = element$linewidth, col = element$colour,
-                       fill = element$fill, lty = element$linetype)
-  pathGrob(
-    x = x, y = y, gp = modify_list(element_gp, gp), ...,
-    # We swap the id logic so that `id` is always the (super)group id
-    # (consistent with `polygonGrob()`) and `pathId` always the subgroup id.
-    pathId = id, pathId.lengths = id.lengths,
-    id = pathId, id.lengths = pathId.lengths
-  )
-}
-
-#' @export
-element_grob.element_point <- function(element, x = 0.5, y = 0.5, colour = NULL,
-                                       shape = NULL, fill = NULL, size = NULL,
-                                       stroke = NULL, ...,
-                                       default.units = "npc") {
-
-  gp <- gg_par(col = colour, fill = fill, pointsize = size, stroke = stroke)
-  element_gp <- gg_par(col = element$colour, fill = element$fill,
-                       pointsize = element$size, stroke = element$stroke)
-  shape <- translate_shape_string(shape %||% element$shape %||% 19)
-  pointsGrob(x = x, y = y, pch = shape, gp = modify_list(element_gp, gp),
-             default.units = default.units, ...)
-}
+S7::method(element_grob, element_point) <-
+  function(element, x = 0.5, y = 0.5, colour = NULL,
+           shape = NULL, fill = NULL, size = NULL,
+           stroke = NULL, ...,
+           default.units = "npc") {
+
+    gp <- gg_par(col = colour, fill = fill, pointsize = size, stroke = stroke)
+    element_gp <- gg_par(col = element@colour, fill = element@fill,
+                         pointsize = element@size, stroke = element@stroke)
+    shape <- translate_shape_string(shape %||% element@shape %||% 19)
+    pointsGrob(x = x, y = y, pch = shape, gp = modify_list(element_gp, gp),
+               default.units = default.units, ...)
+  }
 
 #' Define and register new theme elements
 #'
@@ -476,7 +573,7 @@ element_grob.element_point <- function(element, x = 0.5, y = 0.5, colour = NULL,
 #' # plot panels. To do so, it registers a new theme element `ggxyz.panel.annotation`
 #' register_theme_elements(
 #'   ggxyz.panel.annotation = element_text(color = "blue", hjust = 0.95, vjust = 0.05),
-#'   element_tree = list(ggxyz.panel.annotation = el_def("element_text", "text"))
+#'   element_tree = list(ggxyz.panel.annotation = el_def(element_text, "text"))
 #' )
 #'
 #' # Now the package can define a new coord that includes a panel annotation
@@ -595,8 +692,8 @@ check_element_tree <- function(x, arg = caller_arg(x), call = caller_env()) {
 #' @details
 #' The function `el_def()` is used to define new or modified element types and
 #' element inheritance relationships for the element tree.
-#' @param class The name of the element class. Examples are "element_line" or
-#'  "element_text" or "unit", or one of the two reserved keywords "character" or
+#' @param class The name of the element class. Examples are `element_line` or
+#'  `element_text` or "unit", or one of the two reserved keywords "character" or
 #'  "margin". The reserved keyword "character" implies a character
 #'  or numeric vector, not a class called "character". The keyword
 #'  "margin" implies a unit vector of length 4, as created by [margin()].
@@ -607,6 +704,27 @@ check_element_tree <- function(x, arg = caller_arg(x), call = caller_env()) {
 #' @keywords internal
 #' @export
 el_def <- function(class = NULL, inherit = NULL, description = NULL) {
+  if (is.character(class) && length(class) == 1) {
+    # Swap S3 class name for S7 class object
+    class <- switch(
+      class,
+      element = element,
+      element_blank   = element_blank,
+      element_rect    = element_rect,
+      element_line    = element_line,
+      element_text    = element_text,
+      element_polygon = element_polygon,
+      element_point   = element_point,
+      element_geom    = element_geom,
+      margin          = margin,
+      class
+    )
+  }
+  # margins often occur in c("unit", "margin", "rel"), we cannot use the
+  # S7 class here because we don't support heterogeneous lists
+  if (is.character(class) && length(class) > 1) {
+    class[class == "margin"] <- "ggplot2::margin"
+  }
   list(class = class, inherit = inherit, description = description)
 }
 
@@ -615,43 +733,43 @@ el_def <- function(class = NULL, inherit = NULL, description = NULL) {
 # among them. It should not be read from directly, since users may modify the
 # current element tree stored in ggplot_global$element_tree
 .element_tree <- list(
-  line                = el_def("element_line"),
-  rect                = el_def("element_rect"),
-  text                = el_def("element_text"),
-  point               = el_def("element_point"),
-  polygon             = el_def("element_polygon"),
-  geom                = el_def("element_geom"),
-  title               = el_def("element_text", "text"),
+  line                = el_def(element_line),
+  rect                = el_def(element_rect),
+  text                = el_def(element_text),
+  point               = el_def(element_point),
+  polygon             = el_def(element_polygon),
+  geom                = el_def(element_geom),
+  title               = el_def(element_text, "text"),
   spacing             = el_def("unit"),
   margins             = el_def(c("margin", "unit")),
 
-  axis.line           = el_def("element_line", "line"),
-  axis.text           = el_def("element_text", "text"),
-  axis.title          = el_def("element_text", "title"),
-  axis.ticks          = el_def("element_line", "line"),
+  axis.line           = el_def(element_line, "line"),
+  axis.text           = el_def(element_text, "text"),
+  axis.title          = el_def(element_text, "title"),
+  axis.ticks          = el_def(element_line, "line"),
   legend.key.size     = el_def(c("unit", "rel"), "spacing"),
-  panel.grid          = el_def("element_line", "line"),
-  panel.grid.major    = el_def("element_line", "panel.grid"),
-  panel.grid.minor    = el_def("element_line", "panel.grid"),
-  strip.text          = el_def("element_text", "text"),
-
-  axis.line.x         = el_def("element_line", "axis.line"),
-  axis.line.x.top     = el_def("element_line", "axis.line.x"),
-  axis.line.x.bottom  = el_def("element_line", "axis.line.x"),
-  axis.line.y         = el_def("element_line", "axis.line"),
-  axis.line.y.left    = el_def("element_line", "axis.line.y"),
-  axis.line.y.right   = el_def("element_line", "axis.line.y"),
-  axis.line.theta     = el_def("element_line", "axis.line.x"),
-  axis.line.r         = el_def("element_line", "axis.line.y"),
-
-  axis.text.x         = el_def("element_text", "axis.text"),
-  axis.text.x.top     = el_def("element_text", "axis.text.x"),
-  axis.text.x.bottom  = el_def("element_text", "axis.text.x"),
-  axis.text.y         = el_def("element_text", "axis.text"),
-  axis.text.y.left    = el_def("element_text", "axis.text.y"),
-  axis.text.y.right   = el_def("element_text", "axis.text.y"),
-  axis.text.theta     = el_def("element_text", "axis.text.x"),
-  axis.text.r         = el_def("element_text", "axis.text.y"),
+  panel.grid          = el_def(element_line, "line"),
+  panel.grid.major    = el_def(element_line, "panel.grid"),
+  panel.grid.minor    = el_def(element_line, "panel.grid"),
+  strip.text          = el_def(element_text, "text"),
+
+  axis.line.x         = el_def(element_line, "axis.line"),
+  axis.line.x.top     = el_def(element_line, "axis.line.x"),
+  axis.line.x.bottom  = el_def(element_line, "axis.line.x"),
+  axis.line.y         = el_def(element_line, "axis.line"),
+  axis.line.y.left    = el_def(element_line, "axis.line.y"),
+  axis.line.y.right   = el_def(element_line, "axis.line.y"),
+  axis.line.theta     = el_def(element_line, "axis.line.x"),
+  axis.line.r         = el_def(element_line, "axis.line.y"),
+
+  axis.text.x         = el_def(element_text, "axis.text"),
+  axis.text.x.top     = el_def(element_text, "axis.text.x"),
+  axis.text.x.bottom  = el_def(element_text, "axis.text.x"),
+  axis.text.y         = el_def(element_text, "axis.text"),
+  axis.text.y.left    = el_def(element_text, "axis.text.y"),
+  axis.text.y.right   = el_def(element_text, "axis.text.y"),
+  axis.text.theta     = el_def(element_text, "axis.text.x"),
+  axis.text.r         = el_def(element_text, "axis.text.y"),
 
   axis.ticks.length   = el_def(c("unit", "rel"), "spacing"),
   axis.ticks.length.x = el_def(c("unit", "rel"), "axis.ticks.length"),
@@ -663,28 +781,28 @@ el_def <- function(class = NULL, inherit = NULL, description = NULL) {
   axis.ticks.length.theta = el_def(c("unit", "rel"), "axis.ticks.length.x"),
   axis.ticks.length.r = el_def(c("unit", "rel"), "axis.ticks.length.y"),
 
-  axis.ticks.x        = el_def("element_line", "axis.ticks"),
-  axis.ticks.x.top    = el_def("element_line", "axis.ticks.x"),
-  axis.ticks.x.bottom = el_def("element_line", "axis.ticks.x"),
-  axis.ticks.y        = el_def("element_line", "axis.ticks"),
-  axis.ticks.y.left   = el_def("element_line", "axis.ticks.y"),
-  axis.ticks.y.right  = el_def("element_line", "axis.ticks.y"),
-  axis.ticks.theta    = el_def("element_line", "axis.ticks.x"),
-  axis.ticks.r        = el_def("element_line", "axis.ticks.y"),
-
-  axis.title.x        = el_def("element_text", "axis.title"),
-  axis.title.x.top    = el_def("element_text", "axis.title.x"),
-  axis.title.x.bottom = el_def("element_text", "axis.title.x"),
-  axis.title.y        = el_def("element_text", "axis.title"),
-  axis.title.y.left   = el_def("element_text", "axis.title.y"),
-  axis.title.y.right  = el_def("element_text", "axis.title.y"),
-
-  axis.minor.ticks.x.top    = el_def("element_line", "axis.ticks.x.top"),
-  axis.minor.ticks.x.bottom = el_def("element_line", "axis.ticks.x.bottom"),
-  axis.minor.ticks.y.left   = el_def("element_line", "axis.ticks.y.left"),
-  axis.minor.ticks.y.right  = el_def("element_line", "axis.ticks.y.right"),
-  axis.minor.ticks.theta    = el_def("element_line", "axis.ticks.theta"),
-  axis.minor.ticks.r        = el_def("element_line", "axis.ticks.r"),
+  axis.ticks.x        = el_def(element_line, "axis.ticks"),
+  axis.ticks.x.top    = el_def(element_line, "axis.ticks.x"),
+  axis.ticks.x.bottom = el_def(element_line, "axis.ticks.x"),
+  axis.ticks.y        = el_def(element_line, "axis.ticks"),
+  axis.ticks.y.left   = el_def(element_line, "axis.ticks.y"),
+  axis.ticks.y.right  = el_def(element_line, "axis.ticks.y"),
+  axis.ticks.theta    = el_def(element_line, "axis.ticks.x"),
+  axis.ticks.r        = el_def(element_line, "axis.ticks.y"),
+
+  axis.title.x        = el_def(element_text, "axis.title"),
+  axis.title.x.top    = el_def(element_text, "axis.title.x"),
+  axis.title.x.bottom = el_def(element_text, "axis.title.x"),
+  axis.title.y        = el_def(element_text, "axis.title"),
+  axis.title.y.left   = el_def(element_text, "axis.title.y"),
+  axis.title.y.right  = el_def(element_text, "axis.title.y"),
+
+  axis.minor.ticks.x.top    = el_def(element_line, "axis.ticks.x.top"),
+  axis.minor.ticks.x.bottom = el_def(element_line, "axis.ticks.x.bottom"),
+  axis.minor.ticks.y.left   = el_def(element_line, "axis.ticks.y.left"),
+  axis.minor.ticks.y.right  = el_def(element_line, "axis.ticks.y.right"),
+  axis.minor.ticks.theta    = el_def(element_line, "axis.ticks.theta"),
+  axis.minor.ticks.r        = el_def(element_line, "axis.ticks.r"),
 
   axis.minor.ticks.length = el_def(c("unit", "rel")),
   axis.minor.ticks.length.x = el_def(c("unit", "rel"), "axis.minor.ticks.length"),
@@ -708,25 +826,25 @@ el_def <- function(class = NULL, inherit = NULL, description = NULL) {
     c("unit", "rel"), c("axis.minor.ticks.length.y", "axis.ticks.length.r")
   ),
 
-  legend.background   = el_def("element_rect", "rect"),
+  legend.background   = el_def(element_rect, "rect"),
   legend.margin       = el_def(c("margin", "unit", "rel"), "margins"),
   legend.spacing      = el_def(c("unit", "rel"), "spacing"),
   legend.spacing.x     = el_def(c("unit", "rel"), "legend.spacing"),
   legend.spacing.y     = el_def(c("unit", "rel"), "legend.spacing"),
-  legend.key          = el_def("element_rect", "panel.background"),
+  legend.key          = el_def(element_rect, "panel.background"),
   legend.key.height   = el_def(c("unit", "rel"), "legend.key.size"),
   legend.key.width    = el_def(c("unit", "rel"), "legend.key.size"),
   legend.key.spacing  = el_def(c("unit", "rel"), "spacing"),
   legend.key.spacing.x = el_def(c("unit", "rel"), "legend.key.spacing"),
   legend.key.spacing.y = el_def(c("unit", "rel"), "legend.key.spacing"),
   legend.key.justification = el_def(c("character", "numeric", "integer")),
-  legend.frame        = el_def("element_rect", "rect"),
-  legend.axis.line    = el_def("element_line", "line"),
-  legend.ticks        = el_def("element_line", "legend.axis.line"),
+  legend.frame        = el_def(element_rect, "rect"),
+  legend.axis.line    = el_def(element_line, "line"),
+  legend.ticks        = el_def(element_line, "legend.axis.line"),
   legend.ticks.length = el_def(c("rel", "unit"), "legend.key.size"),
-  legend.text         = el_def("element_text", "text"),
+  legend.text         = el_def(element_text, "text"),
   legend.text.position = el_def("character"),
-  legend.title        = el_def("element_text", "title"),
+  legend.title        = el_def(element_text, "title"),
   legend.title.position = el_def("character"),
   legend.byrow        = el_def("logical"),
   legend.position     = el_def("character"),
@@ -760,45 +878,45 @@ el_def <- function(class = NULL, inherit = NULL, description = NULL) {
   legend.box          = el_def("character"),
   legend.box.just     = el_def("character"),
   legend.box.margin   = el_def(c("margin", "unit", "rel"), "margins"),
-  legend.box.background = el_def("element_rect", "rect"),
+  legend.box.background = el_def(element_rect, "rect"),
   legend.box.spacing  = el_def(c("unit", "rel"), "spacing"),
 
-  panel.background    = el_def("element_rect", "rect"),
-  panel.border        = el_def("element_rect", "rect"),
+  panel.background    = el_def(element_rect, "rect"),
+  panel.border        = el_def(element_rect, "rect"),
   panel.spacing       = el_def(c("unit", "rel"), "spacing"),
   panel.spacing.x     = el_def(c("unit", "rel"), "panel.spacing"),
   panel.spacing.y     = el_def(c("unit", "rel"), "panel.spacing"),
-  panel.grid.major.x  = el_def("element_line", "panel.grid.major"),
-  panel.grid.major.y  = el_def("element_line", "panel.grid.major"),
-  panel.grid.minor.x  = el_def("element_line", "panel.grid.minor"),
-  panel.grid.minor.y  = el_def("element_line", "panel.grid.minor"),
+  panel.grid.major.x  = el_def(element_line, "panel.grid.major"),
+  panel.grid.major.y  = el_def(element_line, "panel.grid.major"),
+  panel.grid.minor.x  = el_def(element_line, "panel.grid.minor"),
+  panel.grid.minor.y  = el_def(element_line, "panel.grid.minor"),
   panel.ontop         = el_def("logical"),
   panel.widths        = el_def("unit"),
   panel.heights       = el_def("unit"),
 
-  strip.background    = el_def("element_rect", "rect"),
-  strip.background.x  = el_def("element_rect", "strip.background"),
-  strip.background.y  = el_def("element_rect", "strip.background"),
+  strip.background    = el_def(element_rect, "rect"),
+  strip.background.x  = el_def(element_rect, "strip.background"),
+  strip.background.y  = el_def(element_rect, "strip.background"),
   strip.clip          = el_def("character"),
-  strip.text.x        = el_def("element_text", "strip.text"),
-  strip.text.x.top    = el_def("element_text", "strip.text.x"),
-  strip.text.x.bottom = el_def("element_text", "strip.text.x"),
-  strip.text.y        = el_def("element_text", "strip.text"),
-  strip.text.y.left   = el_def("element_text", "strip.text.y"),
-  strip.text.y.right  = el_def("element_text", "strip.text.y"),
+  strip.text.x        = el_def(element_text, "strip.text"),
+  strip.text.x.top    = el_def(element_text, "strip.text.x"),
+  strip.text.x.bottom = el_def(element_text, "strip.text.x"),
+  strip.text.y        = el_def(element_text, "strip.text"),
+  strip.text.y.left   = el_def(element_text, "strip.text.y"),
+  strip.text.y.right  = el_def(element_text, "strip.text.y"),
   strip.placement     = el_def("character"),
   strip.placement.x   = el_def("character", "strip.placement"),
   strip.placement.y   = el_def("character", "strip.placement"),
   strip.switch.pad.grid = el_def(c("unit", "rel"), "spacing"),
   strip.switch.pad.wrap = el_def(c("unit", "rel"), "spacing"),
 
-  plot.background     = el_def("element_rect", "rect"),
-  plot.title          = el_def("element_text", "title"),
+  plot.background     = el_def(element_rect, "rect"),
+  plot.title          = el_def(element_text, "title"),
   plot.title.position = el_def("character"),
-  plot.subtitle       = el_def("element_text", "text"),
-  plot.caption        = el_def("element_text", "text"),
+  plot.subtitle       = el_def(element_text, "text"),
+  plot.caption        = el_def(element_text, "text"),
   plot.caption.position = el_def("character"),
-  plot.tag            = el_def("element_text", "text"),
+  plot.tag            = el_def(element_text, "text"),
   plot.tag.position   = el_def(c("character", "numeric", "integer")),  # Need to also accept numbers
   plot.tag.location   = el_def("character"),
   plot.margin         = el_def(c("margin", "unit", "rel"), "margins"),
@@ -843,11 +961,35 @@ check_element <- function(el, elname, element_tree, call = caller_env()) {
   # NULL values for elements are OK
   if (is.null(el)) return()
 
-  if ("margin" %in% eldef$class) {
-    if (!is.unit(el) && length(el) == 4)
-      cli::cli_abort("The {.var {elname}} theme element must be a {.cls unit} vector of length 4.", call = call)
-  } else if (!inherits(el, eldef$class) && !inherits(el, "element_blank")) {
-    cli::cli_abort("The {.var {elname}} theme element must be a {.cls {eldef$class}} object.", call = call)
+  class <- eldef$class
+  if (inherits(class, "S7_class")) {
+    inherit_ok <- S7::S7_inherits(el, class)
+  } else {
+    inherit_ok <- inherits(el, class)
+  }
+
+  if (is.character(class) && any(c("margin", "ggplot2::margin") %in% class)) {
+    if ("rel" %in% class && is.rel(el)) {
+      return()
+    }
+    if (is.unit(el) && length(el) == 4) {
+      return()
+    }
+    cli::cli_abort(
+      "The {.var {elname}} theme element must be a {.cls unit} vector of length 4",
+      call = call
+    )
+  }
+
+  # Maybe we should check that `class` is an element class before approving of
+  # blank elements?
+  if (inherit_ok || is_theme_element(el, "blank")) {
+    return()
   }
-  invisible()
+
+  class_name <- if (inherits(class, "S7_class")) class@name else class
+  cli::cli_abort(
+    "The {.var {elname}} theme element must be a {.cls {class_name}} object.",
+    call = call
+  )
 }
diff --git a/R/theme.R b/R/theme.R
index 8ad12765a0..5f5121d4fd 100644
--- a/R/theme.R
+++ b/R/theme.R
@@ -217,7 +217,7 @@
 #' @param validate `TRUE` to run `check_element()`, `FALSE` to bypass checks.
 #' @export
 #' @seealso
-#'   [+.gg()] and [%+replace%],
+#'   [add_gg()] and [%+replace%],
 #'   [element_blank()], [element_line()],
 #'   [element_rect()], and [element_text()] for
 #'   details of the specific theme elements.
@@ -475,18 +475,14 @@ theme <- function(...,
   # If complete theme set all non-blank elements to inherit from blanks
   if (complete) {
     elements <- lapply(elements, function(el) {
-      if (is_theme_element(el) && !is_theme_element(el, "blank")) {
-        el$inherit.blank <- TRUE
+      if (is_theme_element(el) && S7::prop_exists(el, "inherit.blank")) {
+        S7::prop(el, "inherit.blank") <- TRUE
       }
       el
     })
   }
-  structure(
-    elements,
-    class = c("theme", "gg"),
-    complete = complete,
-    validate = validate
-  )
+
+  class_theme(elements, complete = complete, validate = validate)
 }
 
 fix_theme_deprecations <- function(elements) {
@@ -576,7 +572,7 @@ validate_theme_palettes <- function(elements) {
 
 #' @export
 #' @rdname is_tests
-is_theme <- function(x) inherits(x, "theme")
+is_theme <- function(x) S7::S7_inherits(x, class_theme)
 
 #' @export
 #' @rdname is_tests
@@ -587,12 +583,13 @@ is.theme <- function(x) {
 }
 
 # check whether theme is complete
-is_theme_complete <- function(x) isTRUE(attr(x, "complete", exact = TRUE))
+is_theme_complete <- function(x) {
+  is_theme(x) && isTRUE(x@complete)
+}
 
 # check whether theme should be validated
 is_theme_validate <- function(x) {
-  validate <- attr(x, "validate", exact = TRUE)
-  isTRUE(validate %||% TRUE)
+  !is_theme(x) || isTRUE(x@validate)
 }
 
 check_theme <- function(theme, tree = get_element_tree(), call = caller_env()) {
@@ -632,21 +629,19 @@ complete_theme <- function(theme = NULL, default = theme_get()) {
   }
   check_object(default, is_theme, "a {.cls theme} object")
   theme <- plot_theme(list(theme = theme), default = default)
-
-  # Using `theme(!!!theme)` drops `NULL` entries, so strip most attributes and
-  # construct a new theme
-  attributes(theme) <- list(names = attr(theme, "names"))
-  structure(
-    theme,
-    class = c("theme", "gg"),
-    complete = TRUE, # This theme is complete and has no missing elements
-    validate = FALSE # Settings have already been validated
-  )
+  theme@complete <- TRUE
+  theme@validate <- FALSE
+  theme
 }
 
 # Combine plot defaults with current theme to get complete theme for a plot
 plot_theme <- function(x, default = get_theme()) {
-  theme <- x$theme
+  if (S7::S7_inherits(x)) {
+    theme <- x@theme
+  } else {
+    theme <- x$theme
+  }
+
 
   # apply theme defaults appropriately if needed
   if (is_theme_complete(theme)) {
@@ -708,13 +703,12 @@ add_theme <- function(t1, t2, t2name, call = caller_env()) {
     }
   )
 
-  # make sure the "complete" attribute is set; this can be missing
-  # when t1 is an empty list
-  attr(t1, "complete") <- is_theme_complete(t1)
+  if (!is_theme(t1) && is.list(t1)) {
+    t1 <- theme(!!!t1)
+  }
 
   # Only validate if both themes should be validated
-  attr(t1, "validate") <-
-    is_theme_validate(t1) && is_theme_validate(t2)
+  t1@validate <- is_theme_validate(t1) && is_theme_validate(t2)
 
   t1
 }
@@ -750,7 +744,7 @@ calc_element <- function(element, theme, verbose = FALSE, skip_blank = FALSE,
 
   # If result is element_blank, we skip it if `skip_blank` is `TRUE`,
   # and otherwise we don't inherit anything from parents
-  if (inherits(el_out, "element_blank")) {
+  if (is_theme_element(el_out, "blank")) {
     if (isTRUE(skip_blank)) {
       el_out <- NULL
     } else {
@@ -764,9 +758,17 @@ calc_element <- function(element, theme, verbose = FALSE, skip_blank = FALSE,
 
   # If the element is defined (and not just inherited), check that
   # it is of the class specified in element_tree
-  if (!is.null(el_out) &&
-      !inherits(el_out, element_tree[[element]]$class)) {
-    cli::cli_abort("Theme element {.var {element}} must have class {.cls {ggplot_global$element_tree[[element]]$class}}.", call = call)
+  if (!is.null(el_out)) {
+    class <- element_tree[[element]]$class
+    if (inherits(class, "S7_class")) {
+      if (!S7::S7_inherits(el_out, class)) {
+        cli::cli_abort("Theme element {.var {element}} must have class {.cls {class@name}}.", call = call)
+      }
+    } else {
+      if (!inherits(el_out, class)) {
+        cli::cli_abort("Theme element {.var {element}} must have class {.cls {ggplot_global$element_tree[[element]]$class}}.", call = call)
+      }
+    }
   }
 
   # Get the names of parents from the inheritance tree
@@ -777,15 +779,23 @@ calc_element <- function(element, theme, verbose = FALSE, skip_blank = FALSE,
     if (verbose) cli::cli_inform("nothing (top level)")
 
     # Check that all the properties of this element are non-NULL
-    nullprops <- vapply(el_out, is.null, logical(1))
+    if (is_theme_element(el_out)) {
+      nullprops <- lengths(S7::props(el_out)) == 0
+    } else {
+      nullprops <- vapply(el_out, is.null, logical(1))
+    }
     if (!any(nullprops)) {
       return(el_out) # no null properties, return element as is
     }
 
     # if we have null properties, try to fill in from ggplot_global$theme_default
     el_out <- combine_elements(el_out, ggplot_global$theme_default[[element]])
-    nullprops <- vapply(el_out, is.null, logical(1))
-    if (inherits(el_out, "element_geom")) {
+    if (is_theme_element(el_out)) {
+      nullprops <- lengths(S7::props(el_out)) == 0
+    } else {
+      nullprops <- vapply(el_out, is.null, logical(1))
+    }
+    if (is_theme_element(el_out, "geom")) {
       # Geom elements are expected to have NULL fill/colour, so allow these
       # to be missing
       nullprops[c("colour", "fill")] <- FALSE
@@ -799,15 +809,19 @@ calc_element <- function(element, theme, verbose = FALSE, skip_blank = FALSE,
 
   # Calculate the parent objects' inheritance
   if (verbose) cli::cli_inform("{pnames}")
+
+  # once we've started skipping blanks, we continue doing so until the end of the
+  # recursion; we initiate skipping blanks if we encounter an element that
+  # doesn't inherit blank.
+  skip_blank <- skip_blank ||
+    (!is.null(el_out) && !isTRUE(try_prop(el_out, "inherit.blank")))
+
   parents <- lapply(
     pnames,
     calc_element,
     theme,
     verbose = verbose,
-    # once we've started skipping blanks, we continue doing so until the end of the
-    # recursion; we initiate skipping blanks if we encounter an element that
-    # doesn't inherit blank.
-    skip_blank = skip_blank || (!is.null(el_out) && !isTRUE(el_out$inherit.blank)),
+    skip_blank = skip_blank,
     call = call
   )
 
@@ -833,69 +847,63 @@ calc_element <- function(element, theme, verbose = FALSE, skip_blank = FALSE,
 #' # Adopt size but ignore colour
 #' merge_element(new, old)
 #'
-merge_element <- function(new, old) {
-  UseMethod("merge_element")
-}
+merge_element <- S7::new_generic("merge_element", c("new", "old"))
+
+S7::method(merge_element, list(S7::class_any, S7::class_any))  <-
+  function(new, old, ...) {
+    if (is.null(old) || is_theme_element(old, "blank")) {
+      # If old is NULL or element_blank, then just return new
+      return(new)
+    } else if (is.null(new) || is.character(new) || is.numeric(new) || is.unit(new) ||
+               is.logical(new) || is.function(new)) {
+      # If new is NULL, or a string, numeric vector, unit, or logical, just return it
+      return(new)
+    }
 
-#' @rdname merge_element
-#' @export
-merge_element.default <- function(new, old) {
-  if (is.null(old) || inherits(old, "element_blank")) {
-    # If old is NULL or element_blank, then just return new
-    return(new)
-  } else if (is.null(new) || is.character(new) || is.numeric(new) || is.unit(new) ||
-             is.logical(new) || is.function(new)) {
-    # If new is NULL, or a string, numeric vector, unit, or logical, just return it
-    return(new)
+    # otherwise we can't merge
+    cli::cli_abort("No method for merging {.cls {class(new)[1]}} into {.cls {class(old)[1]}}.")
   }
 
-  # otherwise we can't merge
-  cli::cli_abort("No method for merging {.cls {class(new)[1]}} into {.cls {class(old)[1]}}.")
-}
-
-#' @rdname merge_element
-#' @export
-merge_element.element_blank <- function(new, old) {
-  # If new is element_blank, just return it
-  new
-}
-
-#' @rdname merge_element
-#' @export
-merge_element.element <- function(new, old) {
-  if (is.null(old) || inherits(old, "element_blank")) {
-    # If old is NULL or element_blank, then just return new
-    return(new)
+S7::method(merge_element, list(element_blank, S7::class_any)) <-
+  function(new, old, ...) {
+    # If new is element_blank, just return it
+    new
   }
 
-  # actual merging can only happen if classes match
-  if (!inherits(new, class(old)[1])) {
-    cli::cli_abort("Only elements of the same class can be merged.")
-  }
+S7::method(merge_element, list(element, S7::class_any)) <-
+  function(new, old, ...) {
+    if (is.null(old) || is_theme_element(old, "blank")) {
+      # If old is NULL or element_blank, then just return new
+      return(new)
+    }
+
+    # actual merging can only happen if classes match
+    if (!inherits(new, class(old)[1])) {
+      cli::cli_abort("Only elements of the same class can be merged.")
+    }
 
-  # Override NULL properties of new with the values in old
-  # Get logical vector of NULL properties in new
-  idx <- vapply(new, is.null, logical(1))
-  # Get the names of TRUE items
-  idx <- names(idx[idx])
+    # Override NULL properties of new with the values in old
+    # Get logical vector of NULL properties in new
+    idx <- lengths(S7::props(new)) == 0
+    # Get the names of TRUE items
+    idx <- names(idx[idx])
 
-  # Update non-NULL items
-  new[idx] <- old[idx]
+    # Update non-NULL items
+    S7::props(new)[idx] <- S7::props(old, idx)
 
-  new
+    new
 }
 
-#' @rdname merge_element
-#' @export
-merge_element.margin <- function(new, old) {
-  if (is.null(old) || inherits(old, "element_blank")) {
-    return(new)
-  }
-  if (anyNA(new)) {
-    new[is.na(new)] <- old[is.na(new)]
+S7::method(merge_element, list(margin, S7::class_any)) <-
+  function(new, old, ...) {
+    if (is.null(old) || is_theme_element(old, "blank")) {
+      return(new)
+    }
+    if (anyNA(new)) {
+      new[is.na(new)] <- old[is.na(new)]
+    }
+    new
   }
-  new
-}
 
 #' Combine the properties of two elements
 #'
@@ -907,7 +915,7 @@ merge_element.margin <- function(new, old) {
 combine_elements <- function(e1, e2) {
 
   # If e2 is NULL, nothing to inherit
-  if (is.null(e2) || inherits(e1, "element_blank")) {
+  if (is.null(e2) || is_theme_element(e1, "blank")) {
     return(e1)
   }
 
@@ -930,7 +938,7 @@ combine_elements <- function(e1, e2) {
     return(e1)
   }
 
-  if (inherits(e1, "margin") && inherits(e2, "margin")) {
+  if (is_margin(e1) && is_margin(e2)) {
     if (anyNA(e2)) {
       e2[is.na(e2)] <- unit(0, "pt")
     }
@@ -946,8 +954,8 @@ combine_elements <- function(e1, e2) {
 
   # If e2 is element_blank, and e1 inherits blank inherit everything from e2,
   # otherwise ignore e2
-  if (inherits(e2, "element_blank")) {
-    if (e1$inherit.blank) {
+  if (is_theme_element(e2, "blank")) {
+    if (isTRUE(try_prop(e1, "inherit.blank"))) {
       return(e2)
     } else {
       return(e1)
@@ -955,29 +963,29 @@ combine_elements <- function(e1, e2) {
   }
 
   # If e1 has any NULL properties, inherit them from e2
-  n <- names(e1)[vapply(e1, is.null, logical(1))]
-  e1[n] <- e2[n]
+  n <- S7::prop_names(e1)[lengths(S7::props(e1)) == 0]
+  S7::props(e1)[n] <- S7::props(e2)[n]
 
   # Calculate relative sizes
-  if (is.rel(e1$size)) {
-    e1$size <- e2$size * unclass(e1$size)
+  if (is.rel(try_prop(e1, "size"))) {
+    e1@size <- e2@size * unclass(e1@size)
   }
 
   # Calculate relative linewidth
-  if (is.rel(e1$linewidth)) {
-    e1$linewidth <- e2$linewidth * unclass(e1$linewidth)
+  if (is.rel(try_prop(e1, "linewidth"))) {
+    e1@linewidth <- e2@linewidth * unclass(e1@linewidth)
   }
 
-  if (inherits(e1, "element_text")) {
-    e1$margin <- combine_elements(e1$margin, e2$margin)
+  if (is_theme_element(e1, "text")) {
+    e1@margin <- combine_elements(e1@margin, e2@margin)
   }
 
   # If e2 is 'richer' than e1, fill e2 with e1 parameters
   is_subclass <- !any(inherits(e2, class(e1), which = TRUE) == 0)
   is_subclass <- is_subclass && length(setdiff(class(e2), class(e1)) > 0)
   if (is_subclass) {
-    new <- defaults(e1, e2)
-    e2[names(new)] <- new
+    new <- defaults(S7::props(e1), S7::props(e2))
+    S7::props(e2)[names(new)] <- new
     return(e2)
   }
 
@@ -985,9 +993,9 @@ combine_elements <- function(e1, e2) {
 }
 
 #' @export
-`$.theme` <- function(x, ...) {
+`$.ggplot2::theme` <- function(x, ...) {
   .subset2(x, ...)
 }
 
 #' @export
-print.theme <- function(x, ...) utils::str(x)
+`print.ggplot2::theme` <- function(x, ...) utils::str(x)
diff --git a/R/utilities.R b/R/utilities.R
index 8e6f9d46e9..828c9ab711 100644
--- a/R/utilities.R
+++ b/R/utilities.R
@@ -909,3 +909,13 @@ compute_data_size <- function(data, size, default = 0.9,
   data[[target]] <- res * (default %||% 0.9)
   data
 }
+
+try_prop <- function(object, name, default = NULL) {
+  if (!S7::S7_inherits(object)) {
+    return(default)
+  }
+  if (!S7::prop_exists(object, name)) {
+    return(default)
+  }
+  S7::prop(object, name)
+}
diff --git a/R/zzz.R b/R/zzz.R
index 398cb7d7b6..9bfffde0a6 100644
--- a/R/zzz.R
+++ b/R/zzz.R
@@ -30,6 +30,12 @@ on_load(
     vars <- dplyr::vars
   }
 )
+
+on_load(
+  if (getRversion() > "4.3.0") registerS3method("+", "gg", add_gg)
+)
+
+on_load(S7::methods_register())
 .onLoad <- function(...) {
   run_on_load()
 }
diff --git a/_pkgdown.yml b/_pkgdown.yml
index 5b0505afd8..bd721a1b3d 100644
--- a/_pkgdown.yml
+++ b/_pkgdown.yml
@@ -37,7 +37,7 @@ reference:
   contents:
   - ggplot
   - aes
-  - "`+.gg`"
+  - add_gg
   - ggsave
   - qplot
 
diff --git a/man/aes.Rd b/man/aes.Rd
index ed77c5d39e..adce5c7ad4 100644
--- a/man/aes.Rd
+++ b/man/aes.Rd
@@ -17,8 +17,8 @@ The names for x and y aesthetics are typically omitted because they are so
 common; all other aesthetics must be named.}
 }
 \value{
-A list with class \code{uneval}. Components of the list are either
-quosures or constants.
+An S7 object representing a list with class \code{mapping}. Components of
+the list are either quosures or constants.
 }
 \description{
 Aesthetic mappings describe how variables in the data are mapped to visual
diff --git a/man/class_ggplot.Rd b/man/class_ggplot.Rd
new file mode 100644
index 0000000000..5c299b9d60
--- /dev/null
+++ b/man/class_ggplot.Rd
@@ -0,0 +1,50 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/all-classes.R
+\name{class_ggplot}
+\alias{class_ggplot}
+\title{The ggplot class}
+\usage{
+class_ggplot(
+  data = waiver(),
+  layers = list(),
+  scales = NULL,
+  guides = NULL,
+  mapping = aes(),
+  theme = NULL,
+  coordinates = coord_cartesian(default = TRUE),
+  facet = facet_null(),
+  layout = NULL,
+  labels = labs(),
+  plot_env = parent.frame()
+)
+}
+\arguments{
+\item{data}{A property containing any data coerced by \code{\link[=fortify]{fortify()}}.}
+
+\item{layers}{A list of layer instances created by \code{\link[=layer]{layer()}}.}
+
+\item{scales}{A ScalesList ggproto object.}
+
+\item{guides}{A Guides ggproto object created by \code{\link[=guides]{guides()}}.}
+
+\item{mapping}{A mapping class object created by \code{\link[=aes]{aes()}}.}
+
+\item{theme}{A theme class object created by \code{\link[=theme]{theme()}}.}
+
+\item{coordinates}{A Coord ggproto object created by \verb{coord_*()} family of
+functions.}
+
+\item{facet}{A Facet ggproto object created by \verb{facet_*()} family of
+functions.}
+
+\item{layout}{A Layout ggproto object.}
+
+\item{labels}{A labels object created by \code{\link[=labs]{labs()}}.}
+
+\item{plot_env}{An environment.}
+}
+\description{
+The ggplot class collects the needed information to render a plot.
+This class can be constructed using the \code{\link[=ggplot]{ggplot()}} function.
+}
+\keyword{internal}
diff --git a/man/class_ggplot_built.Rd b/man/class_ggplot_built.Rd
new file mode 100644
index 0000000000..4e87451998
--- /dev/null
+++ b/man/class_ggplot_built.Rd
@@ -0,0 +1,23 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/all-classes.R
+\name{class_ggplot_built}
+\alias{class_ggplot_built}
+\title{The ggplot built class}
+\usage{
+class_ggplot_built(data = NULL, layout = NULL, plot = NULL)
+}
+\arguments{
+\item{data}{A list of plain data frames; one for each layer.}
+
+\item{layout}{A Layout ggproto object.}
+
+\item{plot}{A completed ggplot class object.}
+}
+\description{
+The ggplot built class is an intermediate class and represents a processed
+ggplot object ready for rendering. It is constructed by calling
+\code{\link[=ggplot_build]{ggplot_build()}} on a \link[=class_ggplot]{ggplot} object and is not meant to be
+instantiated directly. The class can be rendered to a gtable object by
+calling the \code{\link[=ggplot_gtable]{ggplot_gtable()}} function on a ggplot built class object.
+}
+\keyword{internal}
diff --git a/man/class_labels.Rd b/man/class_labels.Rd
new file mode 100644
index 0000000000..57788e666d
--- /dev/null
+++ b/man/class_labels.Rd
@@ -0,0 +1,17 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/all-classes.R
+\name{class_labels}
+\alias{class_labels}
+\title{The labels class}
+\usage{
+class_labels(labels)
+}
+\arguments{
+\item{labels}{A named list.}
+}
+\description{
+The labels class holds a list with label information to display as titles
+of plot components. The preferred way to construct an object of the labels
+class is to use the \code{\link[=labs]{labs()}} function.
+}
+\keyword{internal}
diff --git a/man/class_mapping.Rd b/man/class_mapping.Rd
new file mode 100644
index 0000000000..63f75456d3
--- /dev/null
+++ b/man/class_mapping.Rd
@@ -0,0 +1,19 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/all-classes.R
+\name{class_mapping}
+\alias{class_mapping}
+\title{The mapping class}
+\usage{
+class_mapping(x, env = globalenv())
+}
+\arguments{
+\item{x}{A list of quosures and constants.}
+
+\item{env}{An environment for symbols that are not quosures or constants.}
+}
+\description{
+The mapping class holds a list of quoted expressions
+(\link[rlang:topic-quosure]{quosures}) or constants. An object is typically
+constructed using the \code{\link[=aes]{aes()}} function.
+}
+\keyword{internal}
diff --git a/man/class_theme.Rd b/man/class_theme.Rd
new file mode 100644
index 0000000000..ab3a03ef1d
--- /dev/null
+++ b/man/class_theme.Rd
@@ -0,0 +1,22 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/all-classes.R
+\name{class_theme}
+\alias{class_theme}
+\title{The theme class}
+\usage{
+class_theme(elements, complete, validate)
+}
+\arguments{
+\item{elements}{A named list containing theme elements.}
+
+\item{complete}{A boolean value stating whether a theme is complete.}
+
+\item{validate}{A boolean value stating whether a theme should still be
+validated.}
+}
+\description{
+The theme class holds information on how non-data elements of the plot
+should be rendered. The preferred way to construct an object of this class
+is through the \code{\link[=theme]{theme()}} function.
+}
+\keyword{internal}
diff --git a/man/element.Rd b/man/element.Rd
index 84fe10fd20..92046f8267 100644
--- a/man/element.Rd
+++ b/man/element.Rd
@@ -1,6 +1,10 @@
 % Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/theme-elements.R, R/margins.R
-\name{element}
+% Please edit documentation in R/margins.R, R/theme-elements.R
+\name{margin}
+\alias{margin}
+\alias{margin_part}
+\alias{margin_auto}
+\alias{element}
 \alias{element_blank}
 \alias{element_rect}
 \alias{element_line}
@@ -9,11 +13,16 @@
 \alias{element_point}
 \alias{element_geom}
 \alias{rel}
-\alias{margin}
-\alias{margin_part}
-\alias{margin_auto}
 \title{Theme elements}
 \usage{
+margin(t = 0, r = 0, b = 0, l = 0, unit = "pt")
+
+margin_part(t = NA, r = NA, b = NA, l = NA, unit = "pt")
+
+margin_auto(t = 0, r = t, b = t, l = r, unit = "pt")
+
+element()
+
 element_blank()
 
 element_rect(
@@ -22,6 +31,7 @@ element_rect(
   linewidth = NULL,
   linetype = NULL,
   color = NULL,
+  linejoin = NULL,
   inherit.blank = FALSE,
   size = deprecated()
 )
@@ -32,6 +42,7 @@ element_line(
   linetype = NULL,
   lineend = NULL,
   color = NULL,
+  linejoin = NULL,
   arrow = NULL,
   arrow.fill = NULL,
   inherit.blank = FALSE,
@@ -59,6 +70,7 @@ element_polygon(
   linewidth = NULL,
   linetype = NULL,
   color = NULL,
+  linejoin = NULL,
   inherit.blank = FALSE
 )
 
@@ -90,14 +102,13 @@ element_geom(
 )
 
 rel(x)
-
-margin(t = 0, r = 0, b = 0, l = 0, unit = "pt")
-
-margin_part(t = NA, r = NA, b = NA, l = NA, unit = "pt")
-
-margin_auto(t = 0, r = t, b = t, l = r, unit = "pt")
 }
 \arguments{
+\item{t, r, b, l}{Dimensions of each margin. (To remember order, think trouble).}
+
+\item{unit}{Default units of dimensions. Defaults to "pt" so it
+can be most easily scaled with the text.}
+
 \item{fill}{Fill colour. \code{fill_alpha()} can be used to set the transparency
 of the fill.}
 
@@ -111,6 +122,8 @@ integer (0:8), a name (blank, solid, dashed, dotted, dotdash, longdash,
 twodash), or a string with an even number (up to eight) of hexadecimal
 digits which give the lengths in consecutive positions in the string.}
 
+\item{linejoin}{Line join style, one of \code{"round"}, \code{"mitre"} or \code{"bevel"}.}
+
 \item{inherit.blank}{Should this element inherit the existence of an
 \code{element_blank} among its parents? If \code{TRUE} the existence of
 a blank element among its parents will cause this element to be blank as
@@ -119,7 +132,7 @@ calculating final element state.}
 
 \item{size, fontsize, pointsize}{text size in pts, point size in mm.}
 
-\item{lineend}{Line end Line end style (round, butt, square)}
+\item{lineend}{Line end style, one of \code{"round"}, \code{"butt"} or \code{"square"}.}
 
 \item{arrow}{Arrow specification, as created by \code{\link[grid:arrow]{grid::arrow()}}}
 
@@ -154,11 +167,6 @@ is anchored.}
 \item{accent}{Accent colour.}
 
 \item{x}{A single number specifying size relative to parent element.}
-
-\item{t, r, b, l}{Dimensions of each margin. (To remember order, think trouble).}
-
-\item{unit}{Default units of dimensions. Defaults to "pt" so it
-can be most easily scaled with the text.}
 }
 \value{
 An S3 object of class \code{element}, \code{rel}, or \code{margin}.
diff --git a/man/get_theme.Rd b/man/get_theme.Rd
index d3283d0e67..d8198c4197 100644
--- a/man/get_theme.Rd
+++ b/man/get_theme.Rd
@@ -120,5 +120,5 @@ rep_el$text
 
 }
 \seealso{
-\code{\link[=+.gg]{+.gg()}}
+\code{\link[=add_gg]{add_gg()}}
 }
diff --git a/man/gg-add.Rd b/man/gg-add.Rd
index bd5e374caa..560f74de68 100644
--- a/man/gg-add.Rd
+++ b/man/gg-add.Rd
@@ -1,11 +1,11 @@
 % Generated by roxygen2: do not edit by hand
 % Please edit documentation in R/plot-construction.R
-\name{+.gg}
-\alias{+.gg}
+\name{add_gg}
+\alias{add_gg}
 \alias{\%+\%}
 \title{Add components to a plot}
 \usage{
-\method{+}{gg}(e1, e2)
+add_gg(e1, e2)
 
 e1 \%+\% e2
 }
diff --git a/man/ggplot.Rd b/man/ggplot.Rd
index ecb7fe5401..2a119981e7 100644
--- a/man/ggplot.Rd
+++ b/man/ggplot.Rd
@@ -4,7 +4,7 @@
 \alias{ggplot}
 \title{Create a new ggplot}
 \usage{
-ggplot(data = NULL, mapping = aes(), ..., environment = parent.frame())
+ggplot(data, mapping = aes(), ..., environment = parent.frame())
 }
 \arguments{
 \item{data}{Default dataset to use for plot. If not already a data.frame,
diff --git a/man/ggplot_add.Rd b/man/ggplot_add.Rd
index c71d6f863e..d1133d26e2 100644
--- a/man/ggplot_add.Rd
+++ b/man/ggplot_add.Rd
@@ -4,21 +4,19 @@
 \alias{ggplot_add}
 \title{Add custom objects to ggplot}
 \usage{
-ggplot_add(object, plot, object_name)
+ggplot_add(object, plot, ...)
 }
 \arguments{
 \item{object}{An object to add to the plot}
 
 \item{plot}{The ggplot object to add \code{object} to}
-
-\item{object_name}{The name of the object to add}
 }
 \value{
 A modified ggplot object
 }
 \description{
 This generic allows you to add your own methods for adding custom objects to
-a ggplot with \link{+.gg}.
+a ggplot with \link[=add_gg]{+.gg}.
 }
 \details{
 Custom methods for \code{ggplot_add()} are intended to update the \code{plot} variable
@@ -32,10 +30,11 @@ the plot intact.
 }
 \examples{
 # making a new method for the generic
-# in this example, we apply a text element to the text theme setting
-ggplot_add.element_text <- function(object, plot, object_name) {
-  plot + theme(text = object)
-}
+# in this example, we enable adding text elements
+S7::method(ggplot_add, list(element_text, class_ggplot)) <-
+  function(object, plot, ...) {
+    plot + theme(text = object)
+  }
 
 # we can now use `+` to add our object to a plot
 ggplot(mpg, aes(displ, cty)) +
@@ -43,6 +42,5 @@ ggplot(mpg, aes(displ, cty)) +
   element_text(colour = "red")
 
 # clean-up
-rm(ggplot_add.element_text)
 }
 \keyword{internal}
diff --git a/man/is_tests.Rd b/man/is_tests.Rd
index bb0b25e799..c3c0630915 100644
--- a/man/is_tests.Rd
+++ b/man/is_tests.Rd
@@ -1,7 +1,7 @@
 % Generated by roxygen2: do not edit by hand
 % Please edit documentation in R/ggproto.R, R/aes.R, R/geom-.R, R/coord-.R,
-%   R/facet-.R, R/stat-.R, R/theme-elements.R, R/guide-.R, R/layer.R,
-%   R/guides-.R, R/margins.R, R/plot.R, R/position-.R, R/scale-.R, R/theme.R
+%   R/facet-.R, R/stat-.R, R/margins.R, R/theme-elements.R, R/guide-.R,
+%   R/layer.R, R/guides-.R, R/plot.R, R/position-.R, R/scale-.R, R/theme.R
 \name{is_ggproto}
 \alias{is_ggproto}
 \alias{is.ggproto}
@@ -12,11 +12,11 @@
 \alias{is_facet}
 \alias{is.facet}
 \alias{is_stat}
+\alias{is_margin}
 \alias{is_theme_element}
 \alias{is_guide}
 \alias{is_layer}
 \alias{is_guides}
-\alias{is_margin}
 \alias{is_tests}
 \alias{is_ggplot}
 \alias{is.ggplot}
@@ -44,6 +44,8 @@ is.facet(x) # Deprecated
 
 is_stat(x)
 
+is_margin(x)
+
 is_theme_element(x, type = "any")
 
 is_guide(x)
@@ -52,8 +54,6 @@ is_layer(x)
 
 is_guides(x)
 
-is_margin(x)
-
 is_ggplot(x)
 
 is.ggplot(x) # Deprecated
@@ -70,7 +70,7 @@ is.theme(x) # Deprecated
 \item{x}{An object to test}
 
 \item{type}{For testing elements: the type of element to expect. One of
-\code{"blank"}, \code{"rect"}, \code{"line"} or \code{"text"}.}
+\code{"blank"}, \code{"rect"}, \code{"line"}, \code{"text"}, \code{"polygon"}, \code{"point"} or \code{"geom"}.}
 }
 \description{
 Reports wether \code{x} is a type of object
diff --git a/man/merge_element.Rd b/man/merge_element.Rd
index ca993eeec3..3060360dc0 100644
--- a/man/merge_element.Rd
+++ b/man/merge_element.Rd
@@ -2,21 +2,9 @@
 % Please edit documentation in R/theme.R
 \name{merge_element}
 \alias{merge_element}
-\alias{merge_element.default}
-\alias{merge_element.element_blank}
-\alias{merge_element.element}
-\alias{merge_element.margin}
 \title{Merge a parent element into a child element}
 \usage{
-merge_element(new, old)
-
-\method{merge_element}{default}(new, old)
-
-\method{merge_element}{element_blank}(new, old)
-
-\method{merge_element}{element}(new, old)
-
-\method{merge_element}{margin}(new, old)
+merge_element(new, old, ...)
 }
 \arguments{
 \item{new}{The child element in the theme hierarchy}
diff --git a/man/print.ggplot.Rd b/man/print.ggplot.Rd
index 1d558a3e9e..49b2b2dca7 100644
--- a/man/print.ggplot.Rd
+++ b/man/print.ggplot.Rd
@@ -2,12 +2,11 @@
 % Please edit documentation in R/plot.R
 \name{print.ggplot}
 \alias{print.ggplot}
-\alias{plot.ggplot}
+\alias{print.ggplot2::ggplot}
+\alias{plot.ggplot2::ggplot}
 \title{Explicitly draw plot}
 \usage{
-\method{print}{ggplot}(x, newpage = is.null(vp), vp = NULL, ...)
-
-\method{plot}{ggplot}(x, newpage = is.null(vp), vp = NULL, ...)
+\method{print}{`ggplot2::ggplot`}(x, newpage = is.null(vp), vp = NULL, ...)
 }
 \arguments{
 \item{x}{plot to display}
diff --git a/man/register_theme_elements.Rd b/man/register_theme_elements.Rd
index cdbbb25d70..0cb822e686 100644
--- a/man/register_theme_elements.Rd
+++ b/man/register_theme_elements.Rd
@@ -27,8 +27,8 @@ a list of named element definitions created with el_def().}
 \item{reset_current}{If \code{TRUE} (the default), the currently active theme is
 reset to the default theme.}
 
-\item{class}{The name of the element class. Examples are "element_line" or
-"element_text" or "unit", or one of the two reserved keywords "character" or
+\item{class}{The name of the element class. Examples are \code{element_line} or
+\code{element_text} or "unit", or one of the two reserved keywords "character" or
 "margin". The reserved keyword "character" implies a character
 or numeric vector, not a class called "character". The keyword
 "margin" implies a unit vector of length 4, as created by \code{\link[=margin]{margin()}}.}
@@ -76,7 +76,7 @@ element inheritance relationships for the element tree.
 # plot panels. To do so, it registers a new theme element `ggxyz.panel.annotation`
 register_theme_elements(
   ggxyz.panel.annotation = element_text(color = "blue", hjust = 0.95, vjust = 0.05),
-  element_tree = list(ggxyz.panel.annotation = el_def("element_text", "text"))
+  element_tree = list(ggxyz.panel.annotation = el_def(element_text, "text"))
 )
 
 # Now the package can define a new coord that includes a panel annotation
diff --git a/man/summary.ggplot.Rd b/man/summary.ggplot.Rd
deleted file mode 100644
index cf426610bc..0000000000
--- a/man/summary.ggplot.Rd
+++ /dev/null
@@ -1,22 +0,0 @@
-% Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/summary.R
-\name{summary.ggplot}
-\alias{summary.ggplot}
-\title{Displays a useful description of a ggplot object}
-\usage{
-\method{summary}{ggplot}(object, ...)
-}
-\arguments{
-\item{object}{ggplot2 object to summarise}
-
-\item{...}{other arguments ignored (for compatibility with generic)}
-}
-\description{
-Displays a useful description of a ggplot object
-}
-\examples{
-p <- ggplot(mtcars, aes(mpg, wt)) +
-  geom_point()
-summary(p)
-}
-\keyword{internal}
diff --git a/man/theme.Rd b/man/theme.Rd
index 2766a3f8ca..f2a9bdf33f 100644
--- a/man/theme.Rd
+++ b/man/theme.Rd
@@ -519,7 +519,7 @@ p3 + theme(panel.spacing = unit(1, "lines"))
 }
 }
 \seealso{
-\code{\link[=+.gg]{+.gg()}} and \link{\%+replace\%},
+\code{\link[=add_gg]{add_gg()}} and \link{\%+replace\%},
 \code{\link[=element_blank]{element_blank()}}, \code{\link[=element_line]{element_line()}},
 \code{\link[=element_rect]{element_rect()}}, and \code{\link[=element_text]{element_text()}} for
 details of the specific theme elements.
diff --git a/tests/testthat/_snaps/4.0/theme.md b/tests/testthat/_snaps/4.0/theme.md
new file mode 100644
index 0000000000..e4df8865e7
--- /dev/null
+++ b/tests/testthat/_snaps/4.0/theme.md
@@ -0,0 +1,8 @@
+# modifying theme element properties with + operator works
+
+    Code
+      theme_grey() + "asdf"
+    Condition
+      Error in `method(+, list(ggplot2::theme, class_any))`:
+      ! Can't add `"asdf"` to a theme object.
+
diff --git a/tests/testthat/_snaps/4.4/theme.md b/tests/testthat/_snaps/4.4/theme.md
new file mode 100644
index 0000000000..ee5f23ab56
--- /dev/null
+++ b/tests/testthat/_snaps/4.4/theme.md
@@ -0,0 +1,8 @@
+# modifying theme element properties with + operator works
+
+    Code
+      theme_grey() + "asdf"
+    Condition
+      Error:
+      ! Can't add `"asdf"` to a theme object.
+
diff --git a/tests/testthat/_snaps/4.5/theme.md b/tests/testthat/_snaps/4.5/theme.md
new file mode 100644
index 0000000000..ee5f23ab56
--- /dev/null
+++ b/tests/testthat/_snaps/4.5/theme.md
@@ -0,0 +1,8 @@
+# modifying theme element properties with + operator works
+
+    Code
+      theme_grey() + "asdf"
+    Condition
+      Error:
+      ! Can't add `"asdf"` to a theme object.
+
diff --git a/tests/testthat/_snaps/aes.md b/tests/testthat/_snaps/aes.md
index 4a891eacbe..c4b534a453 100644
--- a/tests/testthat/_snaps/aes.md
+++ b/tests/testthat/_snaps/aes.md
@@ -54,7 +54,7 @@
 
     Don't know how to get alternative usage for `foo`.
 
-# new_aes() checks its inputs
+# class_mapping() checks its inputs
 
     `x` must be a <list>, not an integer vector.
 
diff --git a/tests/testthat/_snaps/error.md b/tests/testthat/_snaps/error.md
deleted file mode 100644
index a8cb5172df..0000000000
--- a/tests/testthat/_snaps/error.md
+++ /dev/null
@@ -1,10 +0,0 @@
-# various misuses of +.gg (#2638)
-
-    Cannot use `+` with a single argument.
-    i Did you accidentally put `+` on a new line?
-
----
-
-    Cannot add <ggproto> objects together.
-    i Did you forget to add this object to a <ggplot> object?
-
diff --git a/tests/testthat/_snaps/fortify.md b/tests/testthat/_snaps/fortify.md
index 605829d9d8..5baf41b576 100644
--- a/tests/testthat/_snaps/fortify.md
+++ b/tests/testthat/_snaps/fortify.md
@@ -1,6 +1,6 @@
-# fortify.default proves a helpful error with class uneval
+# fortify.default proves a helpful error with mapping class
 
-    `data` must be a <data.frame>, or an object coercible by `fortify()`, or a valid <data.frame>-like object coercible by `as.data.frame()`, not a <uneval> object.
+    `data` must be a <data.frame>, or an object coercible by `fortify()`, or a valid <data.frame>-like object coercible by `as.data.frame()`, not a <ggplot2::mapping> object.
     i Did you accidentally pass `aes()` to the `data` argument?
 
 # fortify.default can handle healthy data-frame-like objects
diff --git a/tests/testthat/_snaps/prohibited-functions.md b/tests/testthat/_snaps/prohibited-functions.md
index e13510ebcf..fe32ebf1c4 100644
--- a/tests/testthat/_snaps/prohibited-functions.md
+++ b/tests/testthat/_snaps/prohibited-functions.md
@@ -12,6 +12,9 @@
       $calc_element
       [1] "skip_blank"
       
+      $class_ggplot
+      [1] "plot_env"
+      
       $continuous_scale
       [1] "scale_name"   "minor_breaks"
       
@@ -52,9 +55,6 @@
       $geom_violin
       [1] "draw_quantiles"
       
-      $ggplot_add
-      [1] "object_name"
-      
       $ggproto
       [1] "_class"   "_inherit"
       
diff --git a/tests/testthat/_snaps/summarise-plot.md b/tests/testthat/_snaps/summarise-plot.md
index 32582d9366..84128c3b47 100644
--- a/tests/testthat/_snaps/summarise-plot.md
+++ b/tests/testthat/_snaps/summarise-plot.md
@@ -1,12 +1,12 @@
 # summarise_*() throws appropriate errors
 
-    `p` must be a <ggplot_built> object, not the number 10.
+    `p` must be a <ggplot2::ggplot_built> object, not the number 10.
 
 ---
 
-    `p` must be a <ggplot_built> object, not the string "A".
+    `p` must be a <ggplot2::ggplot_built> object, not the string "A".
 
 ---
 
-    `p` must be a <ggplot_built> object, not `TRUE`.
+    `p` must be a <ggplot2::ggplot_built> object, not `TRUE`.
 
diff --git a/tests/testthat/_snaps/theme.md b/tests/testthat/_snaps/theme.md
index 0218bbef51..bd92d95024 100644
--- a/tests/testthat/_snaps/theme.md
+++ b/tests/testthat/_snaps/theme.md
@@ -1,19 +1,3 @@
-# modifying theme element properties with + operator works
-
-    Code
-      theme_grey() + "asdf"
-    Condition
-      Error:
-      ! Can't add `"asdf"` to a theme object.
-
-# replacing theme elements with %+replace% operator works
-
-    Code
-      theme_grey() + "asdf"
-    Condition
-      Error:
-      ! Can't add `"asdf"` to a theme object.
-
 # theme validation happens at build stage
 
     The `text` theme element must be a <element_text> object.
@@ -25,7 +9,7 @@
 # incorrect theme specifications throw meaningful errors
 
     Can't merge the `line` theme element.
-    Caused by error in `merge_element()`:
+    Caused by error in `method(merge_element, list(ggplot2::element, class_any))`:
     ! Only elements of the same class can be merged.
 
 ---
@@ -34,7 +18,7 @@
 
 ---
 
-    Theme element `test` has `NULL` property without default: fill, colour, linewidth, and linetype.
+    Theme element `test` has `NULL` property without default: fill, colour, linewidth, linetype, and linejoin.
 
 ---
 
@@ -74,7 +58,7 @@
     Code
       merge_element(text_base, rect_base)
     Condition
-      Error in `merge_element()`:
+      Error in `method(merge_element, list(ggplot2::element, class_any))`:
       ! Only elements of the same class can be merged.
 
 # Theme elements are checked during build
diff --git a/tests/testthat/helper-plot-data.R b/tests/testthat/helper-plot-data.R
index 13e36d861a..cf97be4122 100644
--- a/tests/testthat/helper-plot-data.R
+++ b/tests/testthat/helper-plot-data.R
@@ -2,23 +2,23 @@
 cdata <- function(plot) {
   pieces <- ggplot_build(plot)
 
-  lapply(pieces$data, function(d) {
+  lapply(pieces@data, function(d) {
     dapply(d, "PANEL", function(panel_data) {
-      scales <- pieces$layout$get_scales(panel_data$PANEL[1])
-      panel_params <- plot$coordinates$setup_panel_params(scales$x, scales$y, params = pieces$layout$coord_params)
-      plot$coordinates$transform(panel_data, panel_params)
+      scales <- pieces@layout$get_scales(panel_data$PANEL[1])
+      panel_params <- plot@coordinates$setup_panel_params(scales$x, scales$y, params = pieces@layout$coord_params)
+      plot@coordinates$transform(panel_data, panel_params)
     })
   })
 }
 
 pranges <- function(plot) {
-  layout <- ggplot_build(plot)$layout
+  layout <- ggplot_build(plot)@layout
 
   x_ranges <- lapply(layout$panel_scales_x, function(scale) scale$get_limits())
   y_ranges <- lapply(layout$panel_scales_y, function(scale) scale$get_limits())
 
 
-  npscales <- plot$scales$non_position_scales()
+  npscales <- plot@scales$non_position_scales()
   npranges <- lapply(npscales$scales$scales, function(scale) scale$get_limits())
 
 
diff --git a/tests/testthat/test-add.R b/tests/testthat/test-add.R
index a860a55845..0c318e6c9e 100644
--- a/tests/testthat/test-add.R
+++ b/tests/testthat/test-add.R
@@ -1,4 +1,4 @@
-test_that("mapping class is preserved when adding uneval objects", {
+test_that("mapping class is preserved when adding mapping objects", {
   p <- ggplot(mtcars) + aes(wt, mpg)
-  expect_identical(class(p$mapping), "uneval")
+  expect_s7_class(p@mapping, class_mapping)
 })
diff --git a/tests/testthat/test-aes.R b/tests/testthat/test-aes.R
index a42b4a3ae1..b0922383cc 100644
--- a/tests/testthat/test-aes.R
+++ b/tests/testthat/test-aes.R
@@ -37,8 +37,8 @@ test_that("aes_q() & aes_string() preserve explicit NULLs", {
 
 test_that("aes_all() converts strings into mappings", {
   expect_equal(
-    aes_all(c("x", "y", "col", "pch")),
-    aes(x, y, colour = col, shape = pch),
+    unclass(aes_all(c("x", "y", "col", "pch"))),
+    unclass(aes(x, y, colour = col, shape = pch)),
     # ignore the environments of quosures
     ignore_attr = TRUE
   )
@@ -67,7 +67,7 @@ test_that("aes evaluated in environment where plot created", {
 
 test_that("constants are not wrapped in quosures", {
   aes <- aes(1L, "foo", 1.5)
-  expect_identical(unclass(aes), list(x = 1L, y = "foo", 1.5))
+  expect_identical(S7::S7_data(aes), list(x = 1L, y = "foo", 1.5))
 })
 
 test_that("assignment methods wrap symbolic objects in quosures", {
@@ -96,13 +96,13 @@ test_that("assignment methods pull unwrap constants from quosures", {
 
 test_that("quosures are squashed when creating default label for a mapping", {
   p <- ggplot(mtcars) + aes(!!quo(identity(!!quo(cyl))))
-  labels <- ggplot_build(p)$plot$labels
+  labels <- ggplot_build(p)@plot@labels
   expect_identical(labels$x, "identity(cyl)")
 })
 
 test_that("labelling doesn't cause error if aesthetic is NULL", {
   p <- ggplot(mtcars) + aes(x = NULL)
-  labels <- ggplot_build(p)$plot$labels
+  labels <- ggplot_build(p)@plot@labels
   expect_identical(labels$x, "x")
 })
 
@@ -195,8 +195,8 @@ test_that("alternative_aes_extract_usage() can inspect the call", {
   expect_snapshot_error(alternative_aes_extract_usage(x))
 })
 
-test_that("new_aes() checks its inputs", {
-  expect_snapshot_error(new_aes(1:5))
+test_that("class_mapping() checks its inputs", {
+  expect_snapshot_error(class_mapping(1:5))
 })
 
 # Visual tests ------------------------------------------------------------
diff --git a/tests/testthat/test-build.R b/tests/testthat/test-build.R
index cdcbe0c6ac..cfb4cf6e4a 100644
--- a/tests/testthat/test-build.R
+++ b/tests/testthat/test-build.R
@@ -2,7 +2,7 @@
 df <- data_frame(x = 1:3, y = 3:1, z = letters[1:3])
 
 test_that("there is one data frame for each layer", {
-  nlayers <- function(x) length(ggplot_build(x)$data)
+  nlayers <- function(x) length(ggplot_build(x)@data)
 
   l1 <- ggplot(df, aes(x, y)) + geom_point()
   l2 <- ggplot(df, aes(x, y)) + geom_point() + geom_line()
diff --git a/tests/testthat/test-coord-.R b/tests/testthat/test-coord-.R
index b0cef2de26..ea80cb5ce1 100644
--- a/tests/testthat/test-coord-.R
+++ b/tests/testthat/test-coord-.R
@@ -8,7 +8,7 @@ test_that("Coord errors on missing methods", {
 
 test_that("clipping is on by default", {
   p <- ggplot()
-  coord <- ggplot_build(p)$layout$coord
+  coord <- ggplot_build(p)@layout$coord
   expect_equal(coord$clip, "on")
 })
 
@@ -30,11 +30,11 @@ test_that("guide names are not removed by `train_panel_guides()`", {
   data <- ggplot_build(gg)
 
   # Excerpt from ggplot_gtable.ggplot_built
-  plot <- data$plot
-  layout <- data$layout
-  data <- data$data
+  plot <- data@plot
+  layout <- data@layout
+  data <- data@data
 
-  layout$setup_panel_guides(guides_list(NULL), plot$layers)
+  layout$setup_panel_guides(guides_list(NULL), plot@layers)
 
   # Line showing change in outcome
   expect_named(layout$panel_params[[1]]$guides$aesthetics, c("x", "y", "x.sec", "y.sec"))
@@ -97,12 +97,12 @@ test_that("coord expand takes a vector", {
   base <- ggplot() + lims(x = c(0, 10), y = c(0, 10))
 
   p <- ggplot_build(base + coord_cartesian(expand = c(TRUE, FALSE, FALSE, TRUE)))
-  pp <- p$layout$panel_params[[1]]
+  pp <- p@layout$panel_params[[1]]
   expect_equal(pp$x.range, c(-0.5, 10))
   expect_equal(pp$y.range, c(0, 10.5))
 
   p <- ggplot_build(base + coord_cartesian(expand = c(top = FALSE, left = FALSE)))
-  pp <- p$layout$panel_params[[1]]
+  pp <- p@layout$panel_params[[1]]
   expect_equal(pp$x.range, c(0, 10.5))
   expect_equal(pp$y.range, c(-0.5, 10))
 
diff --git a/tests/testthat/test-coord-cartesian.R b/tests/testthat/test-coord-cartesian.R
index 5bb16c4cd1..f404094d4a 100644
--- a/tests/testthat/test-coord-cartesian.R
+++ b/tests/testthat/test-coord-cartesian.R
@@ -1,16 +1,16 @@
 test_that("clipping can be turned off and on", {
   # clip on by default
   p <- ggplot() + coord_cartesian()
-  coord <- ggplot_build(p)$layout$coord
+  coord <- ggplot_build(p)@layout$coord
   expect_equal(coord$clip, "on")
 
   # clip can be turned on and off
   p <- ggplot() + coord_cartesian(clip = "off")
-  coord <- ggplot_build(p)$layout$coord
+  coord <- ggplot_build(p)@layout$coord
   expect_equal(coord$clip, "off")
 
   p <- ggplot() + coord_cartesian(clip = "on")
-  coord <- ggplot_build(p)$layout$coord
+  coord <- ggplot_build(p)@layout$coord
   expect_equal(coord$clip, "on")
 })
 
diff --git a/tests/testthat/test-coord-polar.R b/tests/testthat/test-coord-polar.R
index 466162b0f5..28518eddb9 100644
--- a/tests/testthat/test-coord-polar.R
+++ b/tests/testthat/test-coord-polar.R
@@ -55,11 +55,11 @@ test_that("polar distance calculation ignores NA's", {
 test_that("clipping can be turned off and on", {
   # clip can be turned on and off
   p <- ggplot() + coord_polar()
-  coord <- ggplot_build(p)$layout$coord
+  coord <- ggplot_build(p)@layout$coord
   expect_equal(coord$clip, "on")
 
   p <- ggplot() + coord_polar(clip = "off")
-  coord <- ggplot_build(p)$layout$coord
+  coord <- ggplot_build(p)@layout$coord
   expect_equal(coord$clip, "off")
 })
 
@@ -205,7 +205,7 @@ test_that("coord_radial can deal with empty breaks (#6271)", {
       scale_x_continuous(breaks = numeric()) +
       scale_y_continuous(breaks = numeric())
   )
-  guides <- p$layout$panel_params[[1]]$guides$guides
+  guides <- p@layout$panel_params[[1]]$guides$guides
   is_none <- vapply(guides, inherits, logical(1), what = "GuideNone")
   expect_true(all(is_none))
 })
diff --git a/tests/testthat/test-coord-transform.R b/tests/testthat/test-coord-transform.R
index 7621f5ed9c..9a01b709b7 100644
--- a/tests/testthat/test-coord-transform.R
+++ b/tests/testthat/test-coord-transform.R
@@ -28,8 +28,8 @@ test_that("coord_trans() expands axes identically to coord_cartesian()", {
   built_cartesian <- ggplot_build(p + coord_cartesian())
   built_trans <- ggplot_build(p + coord_trans())
 
-  cartesian_params <- built_cartesian$layout$panel_params[[1]]
-  trans_params <- built_trans$layout$panel_params[[1]]
+  cartesian_params <- built_cartesian@layout$panel_params[[1]]
+  trans_params <- built_trans@layout$panel_params[[1]]
 
   expect_identical(cartesian_params$x.range, trans_params$x.range)
   expect_identical(cartesian_params$y.range, trans_params$y.range)
@@ -40,8 +40,8 @@ test_that("coord_trans(expand = FALSE) expands axes identically to coord_cartesi
   built_cartesian <- ggplot_build(p + coord_cartesian(expand = FALSE))
   built_trans <- ggplot_build(p + coord_trans(expand = FALSE))
 
-  cartesian_params <- built_cartesian$layout$panel_params[[1]]
-  trans_params <- built_trans$layout$panel_params[[1]]
+  cartesian_params <- built_cartesian@layout$panel_params[[1]]
+  trans_params <- built_trans@layout$panel_params[[1]]
 
   expect_identical(cartesian_params$x.range, trans_params$x.range)
   expect_identical(cartesian_params$y.range, trans_params$y.range)
@@ -52,8 +52,8 @@ test_that("coord_trans(y = 'log10') expands the x axis identically to scale_y_lo
   built_cartesian <- ggplot_build(p + scale_y_log10())
   built_trans <- ggplot_build(p + coord_trans(y = "log10"))
 
-  cartesian_params <- built_cartesian$layout$panel_params[[1]]
-  trans_params <- built_trans$layout$panel_params[[1]]
+  cartesian_params <- built_cartesian@layout$panel_params[[1]]
+  trans_params <- built_trans@layout$panel_params[[1]]
 
   expect_identical(cartesian_params$y.range, trans_params$y.range)
 })
@@ -65,8 +65,8 @@ test_that("coord_trans() expands axes outside the domain of the axis trans", {
   built_cartesian <- ggplot_build(p + scale_y_sqrt())
   built_trans <- ggplot_build(p + coord_trans(y = "sqrt"))
 
-  cartesian_params <- built_cartesian$layout$panel_params[[1]]
-  trans_params <- built_trans$layout$panel_params[[1]]
+  cartesian_params <- built_cartesian@layout$panel_params[[1]]
+  trans_params <- built_trans@layout$panel_params[[1]]
 
   expect_identical(cartesian_params$y.range, trans_params$y.range)
 })
@@ -78,8 +78,8 @@ test_that("coord_trans() works with the reverse transformation", {
   built_cartesian <- ggplot_build(p + scale_y_reverse())
   built_trans <- ggplot_build(p + coord_trans(y = "reverse"))
 
-  cartesian_params <- built_cartesian$layout$panel_params[[1]]
-  trans_params <- built_trans$layout$panel_params[[1]]
+  cartesian_params <- built_cartesian@layout$panel_params[[1]]
+  trans_params <- built_trans@layout$panel_params[[1]]
 
   expect_identical(cartesian_params$y.range, trans_params$y.range)
 })
@@ -91,8 +91,8 @@ test_that("coord_trans() can reverse discrete axes", {
   built_cartesian <- ggplot_build(p)
   built_trans <- ggplot_build(p + coord_trans(x = "reverse"))
 
-  cartesian_params <- built_cartesian$layout$panel_params[[1]]
-  trans_params <- built_trans$layout$panel_params[[1]]
+  cartesian_params <- built_cartesian@layout$panel_params[[1]]
+  trans_params <- built_trans@layout$panel_params[[1]]
 
   expect_identical(cartesian_params$x.range, -rev(trans_params$x.range))
 })
diff --git a/tests/testthat/test-coord_sf.R b/tests/testthat/test-coord_sf.R
index a684bea20b..3e96f926dd 100644
--- a/tests/testthat/test-coord_sf.R
+++ b/tests/testthat/test-coord_sf.R
@@ -56,7 +56,7 @@ test_that("axis labels are correct for manual breaks", {
       scale_x_continuous(breaks = c(1000, 2000, 3000)) +
       scale_y_continuous(breaks = c(1000, 1500, 2000))
   )
-  graticule <- b$layout$panel_params[[1]]$graticule
+  graticule <- b@layout$panel_params[[1]]$graticule
   expect_identical(
     graticule[graticule$type == "E", ]$degree_label,
     c("1000", "2000", "3000")
@@ -85,7 +85,7 @@ test_that("axis labels can be set manually", {
         labels = c("D", "E", "F")
       )
   )
-  graticule <- b$layout$panel_params[[1]]$graticule
+  graticule <- b@layout$panel_params[[1]]$graticule
   expect_identical(
     graticule[graticule$type == "E", ]$degree_label,
     c("A", "B", "C")
@@ -128,7 +128,7 @@ test_that("factors are treated like character labels and are not parsed", {
         labels = factor(c("1 * degree * N", "1.5 * degree * N", "2 * degree * N"))
       )
   )
-  graticule <- b$layout$panel_params[[1]]$graticule
+  graticule <- b@layout$panel_params[[1]]$graticule
   expect_identical(
     graticule[graticule$type == "E", ]$degree_label,
     c("A", "B", "C")
@@ -156,7 +156,7 @@ test_that("expressions can be mixed with character labels", {
         labels = parse(text = c("10^3", "1.5 %*% 10^3", "2 %*% 10^3"))
       )
   )
-  graticule <- b$layout$panel_params[[1]]$graticule
+  graticule <- b@layout$panel_params[[1]]$graticule
   expect_identical(
     graticule[graticule$type == "E", ]$degree_label,
     as.list(c("A", "B", "C"))
@@ -180,7 +180,7 @@ test_that("expressions can be mixed with character labels", {
         labels = parse(text = c("10^3", "1.5 %*% 10^3", "2 %*% 10^3"))
       )
   )
-  graticule <- b$layout$panel_params[[1]]$graticule
+  graticule <- b@layout$panel_params[[1]]$graticule
   expect_identical(
     graticule[graticule$type == "N", ]$degree_label,
     as.list(c("A", "B", "C"))
@@ -207,7 +207,7 @@ test_that("degree labels are automatically parsed", {
       scale_y_continuous(breaks = c(10, 15, 20))
   )
 
-  graticule <- b$layout$panel_params[[1]]$graticule
+  graticule <- b@layout$panel_params[[1]]$graticule
   expect_setequal(
     graticule[graticule$type == "N", ]$degree,
     c(10, 15, 20)
@@ -343,7 +343,7 @@ test_that("coord_sf() can use function breaks and n.breaks", {
     scale_y_continuous(n.breaks = 4)
 
   b <- ggplot_build(p)
-  grat <- b$layout$panel_params[[1]]$graticule
+  grat <- b@layout$panel_params[[1]]$graticule
 
   expect_equal(
     vec_slice(grat$degree, grat$type == "E"),
diff --git a/tests/testthat/test-error.R b/tests/testthat/test-error.R
deleted file mode 100644
index 8e1424a7f1..0000000000
--- a/tests/testthat/test-error.R
+++ /dev/null
@@ -1,12 +0,0 @@
-test_that("various misuses of +.gg (#2638)", {
-  expect_snapshot_error(
-    {
-      ggplot(mtcars, aes(hwy, displ))
-      + geom_point()
-    }
-  )
-
-  expect_snapshot_error(
-    geom_point() + geom_point()
-  )
-})
diff --git a/tests/testthat/test-facet-labels.R b/tests/testthat/test-facet-labels.R
index 01fe866a92..f755e93aa8 100644
--- a/tests/testthat/test-facet-labels.R
+++ b/tests/testthat/test-facet-labels.R
@@ -1,6 +1,6 @@
 get_labels_matrix <- function(plot, ...) {
   data <- ggplot_build(plot)
-  layout <- data$layout
+  layout <- data@layout
 
   labels <- get_labels_info(layout$facet, layout, ...)
   labeller <- match.fun(layout$facet$params$labeller)
diff --git a/tests/testthat/test-facet-map.R b/tests/testthat/test-facet-map.R
index d6d1d0c79a..4ce6e24329 100644
--- a/tests/testthat/test-facet-map.R
+++ b/tests/testthat/test-facet-map.R
@@ -184,7 +184,7 @@ test_that("grid: missing values are located correctly", {
 
 # Facet order ----------------------------------------------------------------
 
-get_layout <- function(p)  ggplot_build(p)$layout$layout
+get_layout <- function(p)  ggplot_build(p)@layout$layout
 
 # Data with factor f with levels CBA
 d <- data_frame(x = 1:9, y = 1:9,
diff --git a/tests/testthat/test-facet-strips.R b/tests/testthat/test-facet-strips.R
index d13f8d500c..2f1080877f 100644
--- a/tests/testthat/test-facet-strips.R
+++ b/tests/testthat/test-facet-strips.R
@@ -1,13 +1,13 @@
 strip_layout <- function(p) {
   data <- ggplot_build(p)
-  plot <- data$plot
-  layout <- data$layout
-  data <- data$data
+  plot <- data@plot
+  layout <- data@layout
+  data <- data@data
   theme <- plot_theme(plot)
 
-  geom_grobs <- Map(function(l, d) l$draw_geom(d, layout), plot$layers, data)
+  geom_grobs <- Map(function(l, d) l$draw_geom(d, layout), plot@layers, data)
 
-  facet <- layout$render(geom_grobs, data, theme, plot$labels)
+  facet <- layout$render(geom_grobs, data, theme, plot@labels)
   layout <- facet$layout
   strip_layout <- layout[grepl("^strip", layout$name), 1:4]
   as.list(strip_layout)
diff --git a/tests/testthat/test-fortify.R b/tests/testthat/test-fortify.R
index e98edad549..2650884942 100644
--- a/tests/testthat/test-fortify.R
+++ b/tests/testthat/test-fortify.R
@@ -56,7 +56,7 @@ test_that("spatial polygons have correct ordering", {
   )
 })
 
-test_that("fortify.default proves a helpful error with class uneval", {
+test_that("fortify.default proves a helpful error with mapping class", {
   expect_snapshot_error(ggplot(aes(x = x)))
 })
 
diff --git a/tests/testthat/test-geom-.R b/tests/testthat/test-geom-.R
index 6766178f22..02e0ed9710 100644
--- a/tests/testthat/test-geom-.R
+++ b/tests/testthat/test-geom-.R
@@ -53,7 +53,7 @@ test_that("updating geom aesthetic defaults preserves class and order", {
 
   updated_defaults <- GeomPoint$default_aes
 
-  expect_s3_class(updated_defaults, "uneval")
+  expect_s7_class(updated_defaults, class_mapping)
 
   intended_defaults <- original_defaults
   intended_defaults[["colour"]] <- "red"
@@ -75,7 +75,7 @@ test_that("updating stat aesthetic defaults preserves class and order", {
 
   updated_defaults <- StatBin$default_aes
 
-  expect_s3_class(updated_defaults, "uneval")
+  expect_s7_class(updated_defaults, class_mapping)
 
   intended_defaults <- original_defaults
   intended_defaults[["y"]] <- expr(after_stat(density))
diff --git a/tests/testthat/test-geom-boxplot.R b/tests/testthat/test-geom-boxplot.R
index 81d37cc5a9..9d977501ff 100644
--- a/tests/testthat/test-geom-boxplot.R
+++ b/tests/testthat/test-geom-boxplot.R
@@ -3,8 +3,8 @@ test_that("geom_boxplot range includes all outliers", {
   dat <- data_frame(x = 1, y = c(-(1:20) ^ 3, (1:20) ^ 3) )
   p <- ggplot_build(ggplot(dat, aes(x,y)) + geom_boxplot())
 
-  miny <- p$layout$panel_params[[1]]$y.range[1]
-  maxy <- p$layout$panel_params[[1]]$y.range[2]
+  miny <- p@layout$panel_params[[1]]$y.range[1]
+  maxy <- p@layout$panel_params[[1]]$y.range[2]
 
   expect_true(miny <= min(dat$y))
   expect_true(maxy >= max(dat$y))
@@ -12,8 +12,8 @@ test_that("geom_boxplot range includes all outliers", {
   # Unless specifically directed not to
   p <- ggplot_build(ggplot(dat, aes(x, y)) + geom_boxplot(outliers = FALSE))
 
-  miny <- p$layout$panel_params[[1]]$y.range[1]
-  maxy <- p$layout$panel_params[[1]]$y.range[2]
+  miny <- p@layout$panel_params[[1]]$y.range[1]
+  maxy <- p@layout$panel_params[[1]]$y.range[2]
 
   expect_lte(maxy, max(dat$y))
   expect_gte(miny, min(dat$y))
diff --git a/tests/testthat/test-geom-dotplot.R b/tests/testthat/test-geom-dotplot.R
index f7159bdd80..fa43204e67 100644
--- a/tests/testthat/test-geom-dotplot.R
+++ b/tests/testthat/test-geom-dotplot.R
@@ -68,8 +68,8 @@ test_that("when binning on y-axis, limits depend on the panel", {
    b1 <- ggplot_build(p + facet_wrap(~am))
    b2 <- ggplot_build(p + facet_wrap(~am, scales = "free_y"))
 
-   equal_limits1 <- (b1$layout$panel_params[[1]]$y.range == b1$layout$panel_params[[2]]$y.range)
-   equal_limits2 <- (b2$layout$panel_params[[1]]$y.range == b2$layout$panel_params[[2]]$y.range)
+   equal_limits1 <- (b1@layout$panel_params[[1]]$y.range == b1@layout$panel_params[[2]]$y.range)
+   equal_limits2 <- (b2@layout$panel_params[[1]]$y.range == b2@layout$panel_params[[2]]$y.range)
 
    expect_true(all(equal_limits1))
    expect_false(all(equal_limits2))
diff --git a/tests/testthat/test-geom-polygon.R b/tests/testthat/test-geom-polygon.R
index 3cf3636655..eec237f588 100644
--- a/tests/testthat/test-geom-polygon.R
+++ b/tests/testthat/test-geom-polygon.R
@@ -40,9 +40,9 @@ test_that("geom_polygon is closed before munching", {
     coord_polar()
 
   built <- ggplot_build(p)
-  coord <- built$plot$coordinates
-  data  <- built$data[[1]]
-  param <- built$layout$panel_params[[1]]
+  coord <- built@plot@coordinates
+  data  <- built@data[[1]]
+  param <- built@layout$panel_params[[1]]
 
   closed <- coord_munch(coord, data, param, is_closed = TRUE)
   open   <- coord_munch(coord, data, param, is_closed = FALSE)
diff --git a/tests/testthat/test-geom-sf.R b/tests/testthat/test-geom-sf.R
index 29f5da8323..60a6ab49a1 100644
--- a/tests/testthat/test-geom-sf.R
+++ b/tests/testthat/test-geom-sf.R
@@ -30,24 +30,24 @@ test_that("geom_sf() determines the legend type automatically", {
   }
 
   # test the automatic choice
-  expect_true(fun_geom_sf(mp, TRUE)$plot$layers[[1]]$show.legend)
-  expect_identical(fun_geom_sf(mp, TRUE)$plot$layers[[1]]$computed_geom_params$legend, "point")
+  expect_true(fun_geom_sf(mp, TRUE)@plot@layers[[1]]$show.legend)
+  expect_identical(fun_geom_sf(mp, TRUE)@plot@layers[[1]]$computed_geom_params$legend, "point")
 
-  expect_true(fun_geom_sf(mls, TRUE)$plot$layers[[1]]$show.legend)
-  expect_identical(fun_geom_sf(mls, TRUE)$plot$layers[[1]]$computed_geom_params$legend, "line")
+  expect_true(fun_geom_sf(mls, TRUE)@plot@layers[[1]]$show.legend)
+  expect_identical(fun_geom_sf(mls, TRUE)@plot@layers[[1]]$computed_geom_params$legend, "line")
 
-  expect_true(fun_geom_sf(mpol, TRUE)$plot$layers[[1]]$show.legend)
-  expect_identical(fun_geom_sf(mpol, TRUE)$plot$layers[[1]]$computed_geom_params$legend, "other")
+  expect_true(fun_geom_sf(mpol, TRUE)@plot@layers[[1]]$show.legend)
+  expect_identical(fun_geom_sf(mpol, TRUE)@plot@layers[[1]]$computed_geom_params$legend, "other")
 
   # test that automatic choice can be overridden manually
-  expect_true(fun_geom_sf(mp, "point")$plot$layers[[1]]$show.legend)
-  expect_identical(fun_geom_sf(mp, "point")$plot$layers[[1]]$computed_geom_params$legend, "point")
+  expect_true(fun_geom_sf(mp, "point")@plot@layers[[1]]$show.legend)
+  expect_identical(fun_geom_sf(mp, "point")@plot@layers[[1]]$computed_geom_params$legend, "point")
 
-  expect_true(fun_geom_sf(mls, "point")$plot$layers[[1]]$show.legend)
-  expect_identical(fun_geom_sf(mls, "point")$plot$layers[[1]]$computed_geom_params$legend, "point")
+  expect_true(fun_geom_sf(mls, "point")@plot@layers[[1]]$show.legend)
+  expect_identical(fun_geom_sf(mls, "point")@plot@layers[[1]]$computed_geom_params$legend, "point")
 
-  expect_true(fun_geom_sf(mpol, "point")$plot$layers[[1]]$show.legend)
-  expect_identical(fun_geom_sf(mpol, "point")$plot$layers[[1]]$computed_geom_params$legend, "point")
+  expect_true(fun_geom_sf(mpol, "point")@plot@layers[[1]]$show.legend)
+  expect_identical(fun_geom_sf(mpol, "point")@plot@layers[[1]]$computed_geom_params$legend, "point")
 })
 
 test_that("geom_sf() determines the legend type from mapped geometry column", {
@@ -68,12 +68,12 @@ test_that("geom_sf() determines the legend type from mapped geometry column", {
   p <- ggplot_build(
     ggplot(d_sf) + geom_sf(aes(geometry = g_point, colour = "a"))
   )
-  expect_identical(p$plot$layers[[1]]$computed_geom_params$legend, "point")
+  expect_identical(p@plot@layers[[1]]$computed_geom_params$legend, "point")
 
   p <- ggplot_build(
     ggplot(d_sf) + geom_sf(aes(geometry = g_line, colour = "a"))
   )
-  expect_identical(p$plot$layers[[1]]$computed_geom_params$legend, "line")
+  expect_identical(p@plot@layers[[1]]$computed_geom_params$legend, "line")
 })
 
 test_that("geom_sf() removes rows containing missing aes", {
diff --git a/tests/testthat/test-guide-.R b/tests/testthat/test-guide-.R
index 4f66920c3e..e5f9c34bc6 100644
--- a/tests/testthat/test-guide-.R
+++ b/tests/testthat/test-guide-.R
@@ -14,29 +14,29 @@ test_that("plotting does not induce state changes in guides", {
     geom_point() +
     guides
 
-  snapshot <- serialize(as.list(p$guides), NULL)
+  snapshot <- serialize(as.list(p@guides), NULL)
 
   grob <- ggplotGrob(p)
 
-  expect_identical(as.list(p$guides), unserialize(snapshot))
+  expect_identical(as.list(p@guides), unserialize(snapshot))
 })
 
 test_that("adding guides doesn't change plot state", {
 
   p1 <- ggplot(mtcars, aes(disp, mpg))
 
-  expect_length(p1$guides$guides, 0)
+  expect_length(p1@guides$guides, 0)
 
   p2 <- p1 + guides(y = guide_axis(angle = 45))
 
-  expect_length(p1$guides$guides, 0)
-  expect_length(p2$guides$guides, 1)
+  expect_length(p1@guides$guides, 0)
+  expect_length(p2@guides$guides, 1)
 
   p3 <- p2 + guides(y = guide_axis(angle = 90))
 
-  expect_length(p3$guides$guides, 1)
-  expect_equal(p3$guides$guides[[1]]$params$angle, 90)
-  expect_equal(p2$guides$guides[[1]]$params$angle, 45)
+  expect_length(p3@guides$guides, 1)
+  expect_equal(p3@guides$guides[[1]]$params$angle, 90)
+  expect_equal(p2@guides$guides[[1]]$params$angle, 45)
 })
 
 test_that("dots are checked when making guides", {
diff --git a/tests/testthat/test-guide-colorbar.R b/tests/testthat/test-guide-colorbar.R
index 7cfd96a2f1..e9602a4c73 100644
--- a/tests/testthat/test-guide-colorbar.R
+++ b/tests/testthat/test-guide-colorbar.R
@@ -12,10 +12,10 @@ test_that("Colorbar respects show.legend in layer", {
   df <- data_frame(x = 1:3, y = 1)
   p <- ggplot(df, aes(x = x, y = y, color = x)) +
     geom_point(size = 20, shape = 21, show.legend = FALSE)
-  expect_length(ggplot_build(p)$plot$guides$guides, 0L)
+  expect_length(ggplot_build(p)@plot@guides$guides, 0L)
   p <- ggplot(df, aes(x = x, y = y, color = x)) +
     geom_point(size = 20, shape = 21, show.legend = TRUE)
-  expect_length(ggplot_build(p)$plot$guides$guides, 1L)
+  expect_length(ggplot_build(p)@plot@guides$guides, 1L)
 })
 
 test_that("colorsteps and bins checks the breaks format", {
diff --git a/tests/testthat/test-guide-legend.R b/tests/testthat/test-guide-legend.R
index cd2311ee93..dcc7c25e64 100644
--- a/tests/testthat/test-guide-legend.R
+++ b/tests/testthat/test-guide-legend.R
@@ -128,7 +128,7 @@ test_that("legends can be forced to display unrelated geoms", {
     )
 
   b <- ggplot_build(p)
-  legend <- b$plot$guides$params[[1]]
+  legend <- b@plot@guides$params[[1]]
 
   expect_equal(
     legend$decor[[1]]$data$fill,
diff --git a/tests/testthat/test-guides.R b/tests/testthat/test-guides.R
index 1a3a31143a..e939b5427e 100644
--- a/tests/testthat/test-guides.R
+++ b/tests/testthat/test-guides.R
@@ -6,12 +6,12 @@ test_that("guide_none() can be used in non-position scales", {
     scale_color_discrete(guide = guide_none())
 
   built <- ggplot_build(p)
-  plot <- built$plot
-  guides <- guides_list(plot$guides)
+  plot <- built@plot
+  guides <- guides_list(plot@guides)
   guides <- guides$build(
-    plot$scales,
-    plot$layers,
-    plot$labels
+    plot@scales,
+    plot@layers,
+    plot@labels
   )
 
   expect_length(guides$guides, 0)
@@ -156,7 +156,7 @@ test_that("empty guides are dropped", {
   expect_equal(nrow(gd), 0)
 
   # Draw guides
-  guides <- p$plot$guides$assemble(theme_gray())
+  guides <- p@plot@guides$assemble(theme_gray())
 
   # All guide-boxes should be empty
   expect_true(is.zero(guides))
diff --git a/tests/testthat/test-labels.R b/tests/testthat/test-labels.R
index 4befce8af6..28e7c7b403 100644
--- a/tests/testthat/test-labels.R
+++ b/tests/testthat/test-labels.R
@@ -25,16 +25,16 @@ test_that("setting guide labels works", {
     expect_identical(labs(color = "my label")$colour, "my label")
 
     # No extra elements exists
-    expect_equal(labs(title = "my title"),  list(title = "my title"),  ignore_attr = TRUE)   # formal argument
-    expect_equal(labs(colour = "my label"), list(colour = "my label"), ignore_attr = TRUE)   # dot
-    expect_equal(labs(foo = "bar"),         list(foo = "bar"),         ignore_attr = TRUE)   # non-existent param
+    expect_length(labs(title = "my title"),  1)   # formal argument
+    expect_length(labs(colour = "my label"), 1)   # dot
+    expect_length(labs(foo = "bar"), 1)   # non-existent param
 
     # labs() has list-splicing semantics
     params <- list(title = "my title", tag = "A)")
     expect_identical(labs(!!!params)$tag, "A)")
 
     # NULL is preserved
-    expect_equal(labs(title = NULL), list(title = NULL), ignore_attr = TRUE)
+    expect_length(labs(title = NULL), 1)
 
     # ggtitle works in the same way as labs()
     expect_identical(ggtitle("my title")$title, "my title")
@@ -141,15 +141,15 @@ test_that("position axis label hierarchy works as intended", {
     geom_point(size = 5)
 
   p <- ggplot_build(p)
-  resolve_label <- function(x) p$layout$resolve_label(x, p$plot$labels)
+  resolve_label <- function(x) p@layout$resolve_label(x, p@plot@labels)
 
   # In absence of explicit title, get title from mapping
   expect_identical(
-    resolve_label(p$layout$panel_scales_x[[1]]),
+    resolve_label(p@layout$panel_scales_x[[1]]),
     list(secondary = NULL, primary = "foo")
   )
   expect_identical(
-    resolve_label(p$layout$panel_scales_y[[1]]),
+    resolve_label(p@layout$panel_scales_y[[1]]),
     list(primary = "bar", secondary = NULL)
   )
 
@@ -164,9 +164,9 @@ test_that("position axis label hierarchy works as intended", {
   )
 
   # Guide titles overrule scale names
-  p$layout$setup_panel_guides(
+  p@layout$setup_panel_guides(
     guides_list(list(x = guide_axis("quuX"), y = guide_axis("corgE"))),
-    p$plot$layers
+    p@plot@layers
   )
   expect_identical(
     resolve_label(scale_x_continuous("Baz")),
@@ -190,10 +190,10 @@ test_that("position axis label hierarchy works as intended", {
   )
 
   # Secondary guide titles override secondary axis names
-  p$layout$setup_panel_guides(
+  p@layout$setup_panel_guides(
     guides_list(list(x = guide_axis("quuX"), y = guide_axis("corgE"),
                      x.sec = guide_axis("waldo"), y.sec = guide_axis("fred"))),
-    p$plot$layers
+    p@plot@layers
   )
   expect_identical(
     resolve_label(xsec),
@@ -238,38 +238,38 @@ test_that("moving guide positions lets titles follow", {
   p <- ggplot_build(p)
 
   # Default guide positions
-  p$layout$setup_panel_guides(
+  p@layout$setup_panel_guides(
     guides_list(
       list(x = guide_axis("baz", position = "bottom"),
            y = guide_axis("qux", position = "left"))
     ),
-    p$plot$layers
+    p@plot@layers
   )
   labs <- get_labs(p)
   expect <- list(x = "baz", x.sec = NULL, y = "qux", y.sec = NULL)
   expect_identical(labs[names(expect)], expect)
 
   # Guides at secondary positions
-  p$layout$setup_panel_guides(
+  p@layout$setup_panel_guides(
     guides_list(
       list(x = guide_axis("baz", position = "top"),
            y = guide_axis("qux", position = "right"))
     ),
-    p$plot$layers
+    p@plot@layers
   )
   labs <- get_labs(p)
   expect_identical(labs[names(expect)], expect)
 
   # Primary guides at secondary positions with
   # secondary guides at primary positions
-  p$layout$setup_panel_guides(
+  p@layout$setup_panel_guides(
     guides_list(
       list(x = guide_axis("baz", position = "top"),
            y = guide_axis("qux", position = "right"),
            x.sec = guide_axis("quux"),
            y.sec = guide_axis("corge"))
     ),
-    p$plot$layers
+    p@plot@layers
   )
   labs <- get_labs(p)
   expect[c("x.sec", "y.sec")] <- list("quux", "corge")
@@ -288,16 +288,16 @@ test_that("label dictionaries work", {
     ))
   p <- ggplot_build(p)
 
-  x <- p$layout$resolve_label(p$layout$panel_scales_x[[1]], p$plot$labels)
+  x <- p@layout$resolve_label(p@layout$panel_scales_x[[1]], p@plot@labels)
   expect_equal(x$primary, "Displacement")
 
-  y <- p$layout$resolve_label(p$layout$panel_scales_y[[1]], p$plot$labels)
+  y <- p@layout$resolve_label(p@layout$panel_scales_y[[1]], p@plot@labels)
   expect_equal(y$primary, "Miles per gallon")
 
-  shape <- p$plot$guides$get_params("shape")$title
+  shape <- p@plot@guides$get_params("shape")$title
   expect_equal(shape, "Number of cylinders")
 
-  size <- p$plot$guides$get_params("size")$title
+  size <- p@plot@guides$get_params("size")$title
   expect_equal(size, "Rear axle ratio")
 })
 
diff --git a/tests/testthat/test-layer.R b/tests/testthat/test-layer.R
index 0c65c430df..b2b1d3eba9 100644
--- a/tests/testthat/test-layer.R
+++ b/tests/testthat/test-layer.R
@@ -94,10 +94,10 @@ test_that("layers are stateless except for the computed params", {
   df <- data.frame(x = 1:10, y = 1:10)
   p <- ggplot(df) +
     geom_col(aes(x = x, y = y), width = 0.8, fill = "red")
-  col_layer <- as.list(p$layers[[1]])
+  col_layer <- as.list(p@layers[[1]])
   stateless_names <- setdiff(names(col_layer), c("computed_geom_params", "computed_stat_params", "computed_mapping"))
   invisible(ggplotGrob(p))
-  expect_identical(as.list(p$layers[[1]])[stateless_names], col_layer[stateless_names])
+  expect_identical(as.list(p@layers[[1]])[stateless_names], col_layer[stateless_names])
 })
 
 test_that("inherit.aes works", {
@@ -108,7 +108,7 @@ test_that("inherit.aes works", {
     geom_col(aes(x = x, y = y), inherit.aes = FALSE)
   invisible(ggplotGrob(p1))
   invisible(ggplotGrob(p2))
-  expect_identical(p1$layers[[1]]$computed_mapping, p2$layers[[1]]$computed_mapping)
+  expect_identical(p1@layers[[1]]$computed_mapping, p2@layers[[1]]$computed_mapping)
 })
 
 test_that("retransform works on computed aesthetics in `map_statistic`", {
@@ -117,8 +117,8 @@ test_that("retransform works on computed aesthetics in `map_statistic`", {
   expect_equal(get_layer_data(p)$y, c(3, 5))
 
   # To double check: should be original values when `retransform = FALSE`
-  parent <- p$layers[[1]]$stat
-  p$layers[[1]]$stat <- ggproto(NULL, parent, retransform = FALSE)
+  parent <- p@layers[[1]]$stat
+  p@layers[[1]]$stat <- ggproto(NULL, parent, retransform = FALSE)
   expect_equal(get_layer_data(p)$y, c(9, 25))
 })
 
@@ -148,10 +148,10 @@ test_that("layer warns for constant aesthetics", {
 test_that("layer names can be resolved", {
 
   p <- ggplot() + geom_point() + geom_point()
-  expect_equal(names(p$layers), c("geom_point", "geom_point...2"))
+  expect_equal(names(p@layers), c("geom_point", "geom_point...2"))
 
   p <- ggplot() + geom_point(name = "foo") + geom_point(name = "bar")
-  expect_equal(names(p$layers), c("foo", "bar"))
+  expect_equal(names(p@layers), c("foo", "bar"))
 
   l <- geom_point(name = "foobar")
   expect_snapshot(p + l + l, error = TRUE)
diff --git a/tests/testthat/test-plot.R b/tests/testthat/test-plot.R
index 2cccf79034..45a3e1cede 100644
--- a/tests/testthat/test-plot.R
+++ b/tests/testthat/test-plot.R
@@ -5,6 +5,7 @@ test_that("ggplot() throws informative errors", {
 })
 
 test_that("construction have user friendly errors", {
+  skip_if(getRversion() < "4.3.0")
   expect_snapshot_error(+ geom_point())
   expect_snapshot_error(geom_point() + geom_bar())
   expect_snapshot_error(ggplot() + 1)
diff --git a/tests/testthat/test-qplot.R b/tests/testthat/test-qplot.R
index 74ab153c39..59527d1989 100644
--- a/tests/testthat/test-qplot.R
+++ b/tests/testthat/test-qplot.R
@@ -3,20 +3,25 @@ test_that("qplot works with variables in data frame and parent env", {
   y <- 1:10
   b <- 1:10
 
+
   lifecycle::expect_deprecated(
-    expect_s3_class(qplot(x, y, data = df), "ggplot")
+    p <- qplot(x, y, data = df)
   )
+  expect_s7_class(p, class_ggplot)
   lifecycle::expect_deprecated(
-    expect_s3_class(qplot(x, y, data = df, colour = a), "ggplot")
+    p <- qplot(x, y, data = df, colour = a)
   )
+  expect_s7_class(p, class_ggplot)
   lifecycle::expect_deprecated(
-    expect_s3_class(qplot(x, y, data = df, colour = b), "ggplot")
+    p <- qplot(x, y, data = df, colour = b)
   )
+  expect_s7_class(p, class_ggplot)
 
   bin <- 1
   lifecycle::expect_deprecated(
-    expect_s3_class(qplot(x, data = df, binwidth = bin), "ggplot")
+    p <- qplot(x, data = df, binwidth = bin)
   )
+  expect_s7_class(p, class_ggplot)
 })
 
 test_that("qplot works in non-standard environments", {
@@ -27,7 +32,7 @@ test_that("qplot works in non-standard environments", {
       qplot(x, breaks = 0:`-1-`)
     })
   )
-  expect_s3_class(p, "ggplot")
+  expect_s7_class(p, class_ggplot)
 })
 
 test_that("qplot() evaluates constants in the right place", {
diff --git a/tests/testthat/test-scale-discrete.R b/tests/testthat/test-scale-discrete.R
index 50f7b585fe..46e5c83d16 100644
--- a/tests/testthat/test-scale-discrete.R
+++ b/tests/testthat/test-scale-discrete.R
@@ -180,7 +180,7 @@ test_that("palettes work for discrete scales", {
   # Check discsrete expansion is applied
   b <- ggplot_build(p)
   expect_equal(
-    b$layout$panel_params[[1]]$x.range,
+    b@layout$panel_params[[1]]$x.range,
     range(values) + c(-0.6, 0.6)
   )
 })
diff --git a/tests/testthat/test-scale-manual.R b/tests/testthat/test-scale-manual.R
index 324485952b..75f4879607 100644
--- a/tests/testthat/test-scale-manual.R
+++ b/tests/testthat/test-scale-manual.R
@@ -26,7 +26,7 @@ dat <- data_frame(g = c("B","A","A"))
 p <- ggplot(dat, aes(g, fill = g)) + geom_bar()
 col <- c("A" = "red", "B" = "green", "C" = "blue")
 
-cols <- function(x) ggplot_build(x)$data[[1]][, "fill"]
+cols <- function(x) ggplot_build(x)@data[[1]][, "fill"]
 
 test_that("named values work regardless of order", {
   fill_scale <- function(order) scale_fill_manual(values = col[order],
diff --git a/tests/testthat/test-scales.R b/tests/testthat/test-scales.R
index 5f14a7189c..39e9f77624 100644
--- a/tests/testthat/test-scales.R
+++ b/tests/testthat/test-scales.R
@@ -2,10 +2,10 @@ test_that("building a plot does not affect its scales", {
   dat <- data_frame(x = rnorm(20), y = rnorm(20))
 
   p <- ggplot(dat, aes(x, y)) + geom_point()
-  expect_length(p$scales$scales, 0)
+  expect_length(p@scales$scales, 0)
 
   ggplot_build(p)
-  expect_length(p$scales$scales, 0)
+  expect_length(p@scales$scales, 0)
 })
 
 test_that("ranges update only for variables listed in aesthetics", {
@@ -146,18 +146,18 @@ test_that("all-Inf layers are not used for determining the type of scale", {
     geom_point()
 
   b1 <- ggplot_build(p1)
-  expect_s3_class(b1$layout$panel_scales_x[[1]], "ScaleDiscretePosition")
+  expect_s3_class(b1@layout$panel_scales_x[[1]], "ScaleDiscretePosition")
 
   p2 <- ggplot() +
     # If the layer non-Inf value, it's considered
     annotate("rect", xmin = -Inf, xmax = 0, ymin = -Inf, ymax = Inf, fill = "black")
 
   b2 <- ggplot_build(p2)
-  expect_s3_class(b2$layout$panel_scales_x[[1]], "ScaleContinuousPosition")
+  expect_s3_class(b2@layout$panel_scales_x[[1]], "ScaleContinuousPosition")
 })
 
 test_that("scales are looked for in appropriate place", {
-  xlabel <- function(x) ggplot_build(x)$layout$panel_scales_x[[1]]$name
+  xlabel <- function(x) ggplot_build(x)@layout$panel_scales_x[[1]]$name
   p0 <- ggplot(mtcars, aes(mpg, wt)) + geom_point() + scale_x_continuous("0")
   expect_equal(xlabel(p0), "0")
 
@@ -343,12 +343,12 @@ test_that("scale_apply preserves class and attributes", {
 
   # Perform identity transformation via `scale_apply`
   out <- with_bindings(scale_apply(
-    df, "x", "transform", 1:2, plot$layout$panel_scales_x
+    df, "x", "transform", 1:2, plot@layout$panel_scales_x
   )[[1]], `c.baz` = `c.baz`, `[.baz` = `[.baz`, .env = global_env())
 
   # Check that it errors on bad scale ids
   expect_snapshot_error(scale_apply(
-    df, "x", "transform", c(NA, 1), plot$layout$panel_scales_x
+    df, "x", "transform", c(NA, 1), plot@layout$panel_scales_x
   ))
 
   # Check class preservation
@@ -362,7 +362,7 @@ test_that("scale_apply preserves class and attributes", {
   class(df$x) <- "foobar"
 
   out <- with_bindings(scale_apply(
-    df, "x", "transform", 1:2, plot$layout$panel_scales_x
+    df, "x", "transform", 1:2, plot@layout$panel_scales_x
   )[[1]], `c.baz` = `c.baz`, `[.baz` = `[.baz`, .env = global_env())
 
   expect_false(inherits(out, "foobar"))
@@ -755,7 +755,7 @@ test_that("ViewScales can make fixed copies", {
     annotate("point", x = 5, y = 10) +
     scale_x_discrete(labels = c("four-wheel", "forward", "reverse"))
 
-  b1 <- ggplot_build(p1)$layout$panel_params[[1]]
+  b1 <- ggplot_build(p1)@layout$panel_params[[1]]
 
   # We build a second plot with the first plot's scales
   p2 <- ggplot(mpg, aes(drv, cyl)) +
diff --git a/tests/testthat/test-stat-bin.R b/tests/testthat/test-stat-bin.R
index de1c941b1e..5bae36c446 100644
--- a/tests/testthat/test-stat-bin.R
+++ b/tests/testthat/test-stat-bin.R
@@ -241,19 +241,19 @@ test_that("stat_count throws error when both x and y aesthetic present", {
 test_that("stat_count preserves x order for continuous and discrete", {
   # x is numeric
   b <- ggplot_build(ggplot(mtcars, aes(carb)) + geom_bar())
-  expect_identical(b$data[[1]]$x, c(1,2,3,4,6,8))
-  expect_identical(b$data[[1]]$y, c(7,10,3,10,1,1))
+  expect_identical(b@data[[1]]$x, c(1,2,3,4,6,8))
+  expect_identical(b@data[[1]]$y, c(7,10,3,10,1,1))
 
   # x is factor where levels match numeric order
   mtcars$carb2 <- factor(mtcars$carb)
   b <- ggplot_build(ggplot(mtcars, aes(carb2)) + geom_bar())
-  expect_identical(b$data[[1]]$x, mapped_discrete(1:6))
-  expect_identical(b$data[[1]]$y, c(7,10,3,10,1,1))
+  expect_identical(b@data[[1]]$x, mapped_discrete(1:6))
+  expect_identical(b@data[[1]]$y, c(7,10,3,10,1,1))
 
   # x is factor levels differ from numeric order
   mtcars$carb3 <- factor(mtcars$carb, levels = c(4,1,2,3,6,8))
   b <- ggplot_build(ggplot(mtcars, aes(carb3)) + geom_bar())
-  expect_identical(b$data[[1]]$x, mapped_discrete(1:6))
-  expect_identical(b$layout$panel_params[[1]]$x$get_labels(), c("4","1","2","3","6","8"))
-  expect_identical(b$data[[1]]$y, c(10,7,10,3,1,1))
+  expect_identical(b@data[[1]]$x, mapped_discrete(1:6))
+  expect_identical(b@layout$panel_params[[1]]$x$get_labels(), c("4","1","2","3","6","8"))
+  expect_identical(b@data[[1]]$y, c(10,7,10,3,1,1))
 })
diff --git a/tests/testthat/test-stats.R b/tests/testthat/test-stats.R
index f8e8b37f31..6eeeffa938 100644
--- a/tests/testthat/test-stats.R
+++ b/tests/testthat/test-stats.R
@@ -3,12 +3,12 @@ test_that("plot succeeds even if some computation fails", {
   p1 <- ggplot(df, aes(x, y)) + geom_point()
 
   b1 <- ggplot_build(p1)
-  expect_length(b1$data, 1)
+  expect_length(b1@data, 1)
 
   p2 <- p1 + stat_summary(fun = function(x) stop("Failed computation"))
 
   expect_snapshot_warning(b2 <- ggplot_build(p2))
-  expect_length(b2$data, 2)
+  expect_length(b2@data, 2)
 })
 
 test_that("error message is thrown when aesthetics are missing", {
@@ -45,9 +45,9 @@ test_that("erroneously dropped aesthetics are found and issue a warning", {
   )
 
   # colour is dropped because group a's colour is not constant (GeomBar$default_aes$colour is NA)
-  expect_true(all(is.na(b2$data[[1]]$colour)))
+  expect_true(all(is.na(b2@data[[1]]$colour)))
   # fill is dropped because group b's fill is not constant
-  expect_true(all(b2$data[[1]]$fill == "#595959FF"))
+  expect_true(all(b2@data[[1]]$fill == "#595959FF"))
 
   # case 2-1) dropped partially with NA
 
@@ -62,10 +62,10 @@ test_that("erroneously dropped aesthetics are found and issue a warning", {
   expect_snapshot_warning(b3 <- ggplot_build(p3))
 
   # colour is dropped because group a's colour is not constant (GeomBar$default_aes$colour is NA)
-  expect_true(all(is.na(b3$data[[1]]$colour)))
+  expect_true(all(is.na(b3@data[[1]]$colour)))
   # fill is NOT dropped. Group a's fill is na.value, but others are mapped.
   expect_equal(
-    b3$data[[1]]$fill == "#123",
+    b3@data[[1]]$fill == "#123",
     c(TRUE, FALSE, FALSE)
   )
 })
diff --git a/tests/testthat/test-theme.R b/tests/testthat/test-theme.R
index 10ef91cf95..5872e9f14a 100644
--- a/tests/testthat/test-theme.R
+++ b/tests/testthat/test-theme.R
@@ -19,10 +19,10 @@ test_that("modifying theme element properties with + operator works", {
   t <- theme_grey() + theme(axis.title.x = element_text(colour = 'red', margin = margin()))
   expect_identical(t$axis.title.x, element_text(colour = 'red', margin = margin(), vjust = 1))
   # Make sure the theme class didn't change or get dropped
-  expect_s3_class(t, "theme")
+  expect_s7_class(t, class_theme)
   # Make sure the element class didn't change or get dropped
-  expect_s3_class(t$axis.title.x, "element")
-  expect_s3_class(t$axis.title.x, "element_text")
+  expect_s7_class(t$axis.title.x, element)
+  expect_s7_class(t$axis.title.x, element_text)
 
   # Modifying an intermediate node works
   t <- theme_grey() + theme(axis.title = element_text(colour = 'red'))
@@ -30,10 +30,10 @@ test_that("modifying theme element properties with + operator works", {
 
   # Modifying a root node changes only the specified properties
   t <- theme_grey() + theme(text = element_text(colour = 'red'))
-  expect_identical(t$text$colour, 'red')
-  expect_identical(t$text$family, theme_grey()$text$family)
-  expect_identical(t$text$face,   theme_grey()$text$face)
-  expect_identical(t$text$size,   theme_grey()$text$size)
+  expect_identical(t$text@colour, 'red')
+  expect_identical(t$text@family, theme_grey()$text@family)
+  expect_identical(t$text@face,   theme_grey()$text@face)
+  expect_identical(t$text@size,   theme_grey()$text@size)
   # Descendent is unchanged
   expect_identical(t$axis.title.x, theme_grey()$axis.title.x)
 
@@ -49,41 +49,45 @@ test_that("modifying theme element properties with + operator works", {
   t <- theme_grey() + theme()
   expect_identical(t, theme_grey())
 
-  expect_snapshot(theme_grey() + "asdf", error = TRUE)
+  expect_snapshot(
+    theme_grey() + "asdf",
+    error = TRUE,
+    variant = substr(as.character(getRversion()), start = 1, stop = 3)
+  )
 })
 
 test_that("adding theme object to ggplot object with + operator works", {
   ## test with complete theme
   p <- ggplot(data.frame(x = 1:3), aes(x, x)) + geom_point() + theme_grey()
   p <- p + theme(axis.title = element_text(size = 20))
-  expect_true(p$theme$axis.title$size == 20)
+  expect_true(p@theme$axis.title@size == 20)
 
   # Should update specified properties, but not reset other properties
   p <- p + theme(text = element_text(colour = 'red'))
-  expect_true(p$theme$text$colour == 'red')
+  expect_true(p@theme$text@colour == 'red')
   tt <- theme_grey()$text
-  tt$colour <- 'red'
-  expect_true(tt$inherit.blank)
-  tt$inherit.blank <- FALSE
-  expect_identical(p$theme$text, tt)
+  tt@colour <- 'red'
+  expect_true(tt@inherit.blank)
+  tt@inherit.blank <- FALSE
+  expect_identical(p@theme$text, tt)
 
   ## test without complete theme
   p <- ggplot(data.frame(x = 1:3), aes(x, x)) + geom_point()
   p <- p + theme(axis.title = element_text(size = 20))
-  expect_true(p$theme$axis.title$size == 20)
+  expect_true(p@theme$axis.title@size == 20)
 
   # Should update specified properties, but not reset other properties
   p <- p + theme(text = element_text(colour = 'red'))
-  expect_true(p$theme$text$colour == 'red')
-  expect_null(p$theme$text$family)
-  expect_null(p$theme$text$face)
-  expect_null(p$theme$text$size)
-  expect_null(p$theme$text$hjust)
-  expect_null(p$theme$text$vjust)
-  expect_null(p$theme$text$angle)
-  expect_null(p$theme$text$lineheight)
-  expect_null(p$theme$text$margin)
-  expect_null(p$theme$text$debug)
+  expect_true(p@theme$text@colour == 'red')
+  expect_null(p@theme$text@family)
+  expect_null(p@theme$text@face)
+  expect_null(p@theme$text@size)
+  expect_null(p@theme$text@hjust)
+  expect_null(p@theme$text@vjust)
+  expect_null(p@theme$text@angle)
+  expect_null(p@theme$text@lineheight)
+  expect_null(p@theme$text@margin)
+  expect_null(p@theme$text@debug)
 
   ## stepwise addition of partial themes is identical to one-step addition
   p <- ggplot(data.frame(x = 1:3), aes(x, x)) + geom_point()
@@ -95,7 +99,7 @@ test_that("adding theme object to ggplot object with + operator works", {
     theme(axis.line.x = element_line(color = "blue"),
           axis.ticks.x = element_line(color = "red"))
 
-  expect_identical(p1$theme, p2$theme)
+  expect_identical(p1@theme, p2@theme)
 })
 
 test_that("replacing theme elements with %+replace% operator works", {
@@ -103,7 +107,7 @@ test_that("replacing theme elements with %+replace% operator works", {
   t <- theme_grey() %+replace% theme(axis.title.x = element_text(colour = 'red'))
   expect_identical(t$axis.title.x, element_text(colour = 'red'))
   # Make sure the class didn't change or get dropped
-  expect_s3_class(t, "theme")
+  expect_s7_class(t, class_theme)
 
   # Changing an intermediate node works
   t <- theme_grey() %+replace% theme(axis.title = element_text(colour = 'red'))
@@ -114,8 +118,6 @@ test_that("replacing theme elements with %+replace% operator works", {
   # Adding empty theme() has no effect
   t <- theme_grey() %+replace% theme()
   expect_identical(t, theme_grey())
-
-  expect_snapshot(theme_grey() + "asdf", error = TRUE)
 })
 
 test_that("calculating theme element inheritance works", {
@@ -123,36 +125,34 @@ test_that("calculating theme element inheritance works", {
 
   # Check that properties are passed along from axis.title to axis.title.x
   e <- calc_element('axis.title.x', t)
-  expect_identical(e$colour, 'red')
-  expect_false(is.null(e$family))
-  expect_false(is.null(e$face))
-  expect_false(is.null(e$size))
+  expect_identical(e@colour, 'red')
+  expect_false(is.null(e@family))
+  expect_false(is.null(e@face))
+  expect_false(is.null(e@size))
 
   # Check that rel() works for relative sizing, and is applied at each level
   t <- theme_grey(base_size = 12) +
     theme(axis.title   = element_text(size = rel(0.5))) +
     theme(axis.title.x = element_text(size = rel(0.5)))
   e <- calc_element('axis.title', t)
-  expect_identical(e$size, 6)
+  expect_identical(e@size, 6)
   ex <- calc_element('axis.title.x', t)
-  expect_identical(ex$size, 3)
+  expect_identical(ex@size, 3)
 
   # Check that a theme_blank in a parent node gets passed along to children
   t <- theme_grey() + theme(text = element_blank())
   expect_identical(calc_element('axis.title.x', t), element_blank())
 
   # Check that inheritance from derived class works
-  element_dummyrect <- function(dummy) { # like element_rect but w/ dummy argument
-    structure(list(
-      fill = NULL, colour = NULL, dummy = dummy, linewidth = NULL,
-      linetype = NULL, inherit.blank = FALSE
-    ), class = c("element_dummyrect", "element_rect", "element"))
-  }
+  element_dummyrect <- S7::new_class(
+    "element_dummyrect", parent = element_rect,
+    properties = c(element_rect@properties, list(dummy = S7::class_any))
+  )
 
   e <- calc_element(
     "panel.background",
     theme(
-      rect = element_rect(fill = "white", colour = "black", linewidth = 0.5, linetype = 1),
+      rect = element_rect(fill = "white", colour = "black", linewidth = 0.5, linetype = 1, linejoin = "round"),
       panel.background = element_dummyrect(dummy = 5),
       complete = TRUE # need to prevent pulling in default theme
     )
@@ -160,10 +160,10 @@ test_that("calculating theme element inheritance works", {
 
   expect_identical(
     e,
-    structure(list(
-      fill = "white", colour = "black", dummy = 5, linewidth = 0.5, linetype = 1,
+    element_dummyrect(
+      fill = "white", colour = "black", dummy = 5, linewidth = 0.5, linetype = 1, linejoin = "round",
       inherit.blank = TRUE # this is true because we're requesting a complete theme
-    ), class = c("element_dummyrect", "element_rect", "element"))
+    )
   )
 
   # Check that blank elements are skipped in inheritance tree if and only if elements
@@ -175,7 +175,7 @@ test_that("calculating theme element inheritance works", {
     )
   e1 <- calc_element("strip.text.x", t)
   e2 <- calc_element("text", t)
-  e2$inherit.blank <- FALSE # b/c inherit.blank = TRUE for complete themes
+  e2@inherit.blank <- FALSE # b/c inherit.blank = TRUE for complete themes
   expect_identical(e1, e2)
 
   theme <- theme_gray() +
@@ -201,18 +201,18 @@ test_that("complete and non-complete themes interact correctly with each other",
   # But for _element properties_, the one on the right modifies the one on the left.
   t <- theme_bw() + theme(text = element_text(colour = 'red'))
   expect_true(attr(t, "complete"))
-  expect_equal(t$text$colour, 'red')
+  expect_equal(t$text@colour, 'red')
 
   # A complete theme object (like theme_bw) always trumps a non-complete theme object
   t <- theme(text = element_text(colour = 'red')) + theme_bw()
   expect_true(attr(t, "complete"))
-  expect_equal(t$text$colour, theme_bw()$text$colour)
+  expect_equal(t$text@colour, theme_bw()$text@colour)
 
   # Adding two non-complete themes: the one on the right modifies the one on the left.
   t <- theme(text = element_text(colour = 'blue')) +
     theme(text = element_text(colour = 'red'))
   expect_false(attr(t, "complete"))
-  expect_equal(t$text$colour, 'red')
+  expect_equal(t$text@colour, 'red')
 })
 
 test_that("complete and non-complete themes interact correctly with ggplot objects", {
@@ -221,33 +221,33 @@ test_that("complete and non-complete themes interact correctly with ggplot objec
   # Check that adding two theme successive theme objects to a ggplot object
   # works like adding the two theme object to each other
   p <- ggplot_build(base + theme_bw() + theme(text = element_text(colour = 'red')))
-  expect_true(attr(p$plot$theme, "complete"))
+  expect_true(attr(p@plot@theme, "complete"))
 
   # Compare the theme objects, after sorting the items, because item order can differ
-  pt <- p$plot$theme
+  pt <- p@plot@theme
   tt <- theme_bw() + theme(text = element_text(colour = 'red'))
   pt <- pt[order(names(pt))]
   tt <- tt[order(names(tt))]
   expect_identical(pt, tt)
 
   p <- ggplot_build(base + theme(text = element_text(colour = 'red')) + theme_bw())
-  expect_true(attr(p$plot$theme, "complete"))
+  expect_true(attr(p@plot@theme, "complete"))
   # Compare the theme objects, after sorting the items, because item order can differ
-  pt <- p$plot$theme
+  pt <- p@plot@theme
   tt <- theme(text = element_text(colour = 'red')) + theme_bw()
   pt <- pt[order(names(pt))]
   tt <- tt[order(names(tt))]
   expect_identical(pt, tt)
 
   p <- ggplot_build(base + theme(text = element_text(colour = 'red', face = 'italic')))
-  expect_equal(p$plot$theme$text$colour, "red")
-  expect_equal(p$plot$theme$text$face, "italic")
+  expect_equal(p@plot@theme$text@colour, "red")
+  expect_equal(p@plot@theme$text@face, "italic")
 
   p <- ggplot_build(base +
     theme(text = element_text(colour = 'red')) +
     theme(text = element_text(face = 'italic')))
-  expect_equal(p$plot$theme$text$colour, "red")
-  expect_equal(p$plot$theme$text$face, "italic")
+  expect_equal(p@plot@theme$text@colour, "red")
+  expect_equal(p@plot@theme$text@face, "italic")
 })
 
 test_that("theme(validate=FALSE) means do not check_element", {
@@ -255,16 +255,16 @@ test_that("theme(validate=FALSE) means do not check_element", {
   bw <- p + theme_bw()
   red.text <- theme(text = element_text(colour = "red"))
   bw.before <- bw + theme(animint.width = 500, validate = FALSE)
-  expect_equal(bw.before$theme$animint.width, 500)
+  expect_equal(bw.before@theme$animint.width, 500)
 
   bw.after <- p + theme(animint.width = 500, validate = FALSE) + theme_bw()
-  expect_null(bw.after$theme$animint.width)
+  expect_null(bw.after@theme$animint.width)
 
   red.after <- p + theme(animint.width = 500, validate = FALSE) + red.text
-  expect_equal(red.after$theme$animint.width, 500)
+  expect_equal(red.after@theme$animint.width, 500)
 
   red.before <- p + red.text + theme(animint.width = 500, validate = FALSE)
-  expect_equal(red.before$theme$animint.width, 500)
+  expect_equal(red.before@theme$animint.width, 500)
 })
 
 test_that("theme validation happens at build stage", {
@@ -283,9 +283,10 @@ test_that("theme validation happens at build stage", {
 test_that("incorrect theme specifications throw meaningful errors", {
   expect_snapshot_error(add_theme(theme_grey(), theme(line = element_rect())))
   expect_snapshot_error(calc_element("line", theme(line = element_rect())))
-  register_theme_elements(element_tree = list(test = el_def("element_rect")))
+  register_theme_elements(element_tree = list(test = el_def(element_rect)))
   expect_snapshot_error(calc_element("test", theme_gray() + theme(test = element_rect())))
   expect_snapshot_error(set_theme("foo"))
+  reset_theme_settings()
 })
 
 test_that("element tree can be modified", {
@@ -305,7 +306,7 @@ test_that("element tree can be modified", {
 
   # things work once we add a new element to the element tree
   register_theme_elements(
-    element_tree = list(blablabla = el_def("element_text", "text"))
+    element_tree = list(blablabla = el_def(element_text, "text"))
   )
   expect_silent(ggplotGrob(p))
 
@@ -327,31 +328,29 @@ test_that("element tree can be modified", {
   final_theme <- ggplot2:::plot_theme(p, theme_gray())
   e1 <- calc_element("blablabla", final_theme)
   e2 <- calc_element("text", final_theme)
-  expect_identical(e1$family, e2$family)
-  expect_identical(e1$face, e2$face)
-  expect_identical(e1$size, e2$size)
-  expect_identical(e1$lineheight, e2$lineheight)
-  expect_identical(e1$colour, "red") # not inherited from element_text
+  expect_identical(e1@family, e2@family)
+  expect_identical(e1@face, e2@face)
+  expect_identical(e1@size, e2@size)
+  expect_identical(e1@lineheight, e2@lineheight)
+  expect_identical(e1@colour, "red") # not inherited from element_text
 
   # existing elements can be overwritten
-  ed <- el_def("element_rect", "rect")
+  ed <- el_def(element_rect, "rect")
   register_theme_elements(
     element_tree = list(axis.title = ed)
   )
   expect_identical(get_element_tree()$axis.title, ed)
 
-  reset_theme_settings(reset_current = FALSE) # revert back to defaults
+  reset_theme_settings() # revert back to defaults
 })
 
 test_that("all elements in complete themes have inherit.blank=TRUE", {
   inherit_blanks <- function(theme) {
-    all(vapply(theme, function(el) {
-      if (is_theme_element(el) && !is_theme_element(el, "blank")) {
-        el$inherit.blank
-      } else {
-        TRUE
-      }
-    }, logical(1)))
+    all(vapply(
+      theme, try_prop,
+      name = "inherit.blank", default = TRUE,
+      logical(1)
+    ))
   }
   expect_true(inherit_blanks(theme_grey()))
   expect_true(inherit_blanks(theme_bw()))
@@ -393,7 +392,7 @@ test_that("complete plot themes shouldn't inherit from default", {
   base <- ggplot(data.frame(x = 1), aes(x, x)) + geom_point()
 
   ptheme <- plot_theme(base + theme(axis.text.x = element_text(colour = "blue")), default_theme)
-  expect_equal(ptheme$axis.text.x$colour, "blue")
+  expect_equal(ptheme$axis.text.x@colour, "blue")
 
   ptheme <- plot_theme(base + theme_void(), default_theme)
   expect_null(ptheme$axis.text.x)
@@ -423,14 +422,14 @@ test_that("current theme can be updated with new elements", {
   # element tree gets merged properly
   register_theme_elements(
     abcde = element_text(color = "blue", hjust = 0, vjust = 1),
-    element_tree = list(abcde = el_def("element_text", "text"))
+    element_tree = list(abcde = el_def(element_text, "text"))
   )
 
   e1 <- calc_element("abcde", plot_theme(b2))
   e2 <- calc_element("text", plot_theme(b2))
-  e2$colour <- "blue"
-  e2$hjust <- 0
-  e2$vjust <- 1
+  e2@colour <- "blue"
+  e2@hjust <- 0
+  e2@vjust <- 1
   expect_identical(e1, e2)
 
   reset_theme_settings()
@@ -565,7 +564,7 @@ test_that("Element subclasses are inherited", {
   test <- combine_elements(poor, rich)
   expect_s3_class(test, "element_rich")
   expect_equal(
-    test[c("colour", "linetype", "linewidth")],
+    S7::props(test)[c("colour", "linetype", "linewidth")],
     list(colour = "red", linetype = 3, linewidth = 2)
   )
 
@@ -573,7 +572,7 @@ test_that("Element subclasses are inherited", {
   test <- combine_elements(rich, poor)
   expect_s3_class(test, "element_rich")
   expect_equal(
-    test[c("colour", "linetype", "linewidth")],
+    S7::props(test)[c("colour", "linetype", "linewidth")],
     list(colour = "red", linetype = 2, linewidth = 2)
   )
 
@@ -585,7 +584,7 @@ test_that("Element subclasses are inherited", {
   test <- combine_elements(sibling, rich)
   expect_s3_class(test, "element_sibling")
   expect_equal(
-    test[c("colour", "linetype", "linewidth")],
+    S7::props(test)[c("colour", "linetype", "linewidth")],
     list(colour = "red", linetype = 3, linewidth = 2)
   )
 
@@ -593,7 +592,7 @@ test_that("Element subclasses are inherited", {
   test <- combine_elements(rich, sibling)
   expect_s3_class(test, "element_rich")
   expect_equal(
-    test[c("colour", "linetype", "linewidth")],
+    S7::props(test)[c("colour", "linetype", "linewidth")],
     list(colour = "red", linetype = 2, linewidth = 2)
   )
 })
@@ -620,33 +619,33 @@ test_that("header_family is passed on correctly", {
   td <- theme_dark(base_family = "x", header_family = "y")
 
   test <- calc_element("plot.title", td)
-  expect_equal(test$family, "y")
+  expect_equal(test@family, "y")
 
   test <- calc_element("plot.subtitle", td)
-  expect_equal(test$family, "x")
+  expect_equal(test@family, "x")
 })
 
 test_that("complete_theme completes a theme", {
   # `NULL` should match default
   gray <- theme_gray()
   new <- complete_theme(NULL, default = gray)
-  expect_equal(new, gray, ignore_attr = "validate")
+  expect_equal(S7::S7_data(new), S7::S7_data(gray))
 
   # Elements are propagated
   new <- complete_theme(theme(axis.line = element_line("red")), gray)
-  expect_equal(new$axis.line$colour, "red")
+  expect_equal(new$axis.line@colour, "red")
 
   # Missing elements are filled in if default theme is incomplete
   new <- complete_theme(default = theme())
-  expect_s3_class(new$axis.line, "element_blank")
+  expect_s3_class(new$axis.line, "ggplot2::element_blank")
 
   # Registered elements are included
   register_theme_elements(
     test = element_text(),
-    element_tree = list(test = el_def("element_text", "text"))
+    element_tree = list(test = el_def(element_text, "text"))
   )
   new <- complete_theme(default = gray)
-  expect_s3_class(new$test, "element_text")
+  expect_s3_class(new$test, "ggplot2::element_text")
   reset_theme_settings()
 })
 
@@ -983,15 +982,11 @@ test_that("Legends can on all sides of the plot with custom justification", {
 })
 
 test_that("Strips can render custom elements", {
-  element_test <- function(...) {
-    el <- element_text(...)
-    class(el) <- c("element_test", "element_text", "element")
-    el
-  }
-  element_grob.element_test <- function(element, label = "", x = NULL, y = NULL, ...) {
-    rectGrob(width = unit(1, "cm"), height = unit(1, "cm"))
-  }
-  registerS3method("element_grob", "element_test", element_grob.element_test)
+  element_test <- S7::new_class("element_test", element_text)
+  S7::method(element_grob, element_test) <-
+    function(element, label = "", x = NULL, y = NULL, ...) {
+      rectGrob(width = unit(1, "cm"), height = unit(1, "cm"))
+    }
 
   df <- data_frame(x = 1:3, y = 1:3, a = letters[1:3])
   plot <- ggplot(df, aes(x, y)) +
diff --git a/vignettes/articles/faq-axes.Rmd b/vignettes/articles/faq-axes.Rmd
index cf88240cfa..1f08b48dce 100644
--- a/vignettes/articles/faq-axes.Rmd
+++ b/vignettes/articles/faq-axes.Rmd
@@ -444,6 +444,8 @@ ggplot(mpg, aes(x = cty^2, y = log(hwy, base = 10))) +
   )
 ```
 
+<!-- Temporarily disabled while migrating to S7
+
 -   If you're already familiar with Markdown and HTML, you might prefer using the [ggtext](https://wilkelab.org/ggtext/) package instead. In Markdown we can write the axis labels as `cty<sup>2</sup>` and `log<sub>10</sub>(hwy)` for x and y axes, respectively. Then, we tell ggplot2 to interpret the axis labels as Markdown and not as plain text by setting `axis.title.x` and `axis.title.y` to `ggtext::element_markdown()`.
 
 ```{r}
@@ -463,6 +465,7 @@ ggplot(mpg, aes(x = cty^2, y = log(hwy, base = 10))) +
     axis.title.y = ggtext::element_markdown()
     )
 ```
+-->
 
 </details>