Apply suggestions from code review

Co-authored-by: Addison Phillips <[email protected]>

Author: eemeli

exploration/0002-expression-attributes.md

@@ -61,11 +61,16 @@ Attributes are distinct from function options.
 Common attributes are defined by the MF2 specification
 and must be supported by all implementations.
 
-Attributes should be user-definable.
+Users may define their own attributes.
 
-Attributes with a runtime impact should not be considered comments.
+Implementations may define their own attributes.
 
-Attributes should relate to a specific expression.
+Some attributes may have an effect on the formatting of an expression.
+These cannot be defined within comments either within or outside a message.
+
+Each attribute relates to a specific expression.
+
+An attribute's scope is limited to the expression to which it relates.
 
 Multiple attributes should be assignable to a single expression.
 
@@ -83,6 +88,10 @@ the reserved/private-use rules will need to be adjusted to support attributes.
 
 Add support for option-like `@key=value` attribute pairs at the end of any expression.
 
+If the syntax for function options is extended to support flag-like options
+(see <a href="https://github.com/unicode-org/message-format-wg/issues/386">#386</a>),
+also extend expression attribute syntax to match.
+
 To distinguish expression attributes from options,
 require `@` as a prefix for each attribute asignment.
 Examples: `@translate=yes` and `@locale=$exprLocale`.