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Allow colon in name-start, matching XML Name #483

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Allow colon in name-start, matching XML Name #483

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14 changes: 8 additions & 6 deletions spec/message.abnf
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Original file line number Diff line number Diff line change
Expand Up @@ -39,8 +39,11 @@ quoted-char = %x0-5B ; omit \
; based on https://www.w3.org/TR/xml/#NT-Nmtoken,
; but cannot start with U+002D HYPHEN-MINUS or U+003A COLON ":"
unquoted = unquoted-start *name-char
unquoted-start = name-start / DIGIT / "."
/ %xB7 / %x300-36F / %x203F-2040
unquoted-start = ALPHA / DIGIT / "." / "_"
/ %xB7 / %xC0-D6 / %xD8-F6 / %xF8-37D
/ %x37F-1FFF / %x200C-200D / %x203F-2040
/ %x2070-218F / %x2C00-2FEF / %x3001-D7FF
/ %xF900-FDCF / %xFDF0-FFFD / %x10000-EFFFF


; reserve sigils for private-use by implementations
Expand All @@ -61,15 +64,14 @@ reserved-char = %x00-08 ; omit HTAB and LF
/ %x7E-D7FF ; omit surrogates
/ %xE000-10FFFF

; based on https://www.w3.org/TR/xml/#NT-Name,
; but cannot start with U+003A COLON ":"
; matches https://www.w3.org/TR/xml/#NT-Name
name = name-start *name-char
name-start = ALPHA / "_"
name-start = ALPHA / ":" / "_"
/ %xC0-D6 / %xD8-F6 / %xF8-2FF
/ %x370-37D / %x37F-1FFF / %x200C-200D
/ %x2070-218F / %x2C00-2FEF / %x3001-D7FF
/ %xF900-FDCF / %xFDF0-FFFD / %x10000-EFFFF
name-char = name-start / DIGIT / "-" / "." / ":"
name-char = name-start / DIGIT / "-" / "."
/ %xB7 / %x300-36F / %x203F-2040

text-escape = backslash ( backslash / "{" / "}" )
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19 changes: 11 additions & 8 deletions spec/syntax.md
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Original file line number Diff line number Diff line change
Expand Up @@ -619,31 +619,34 @@ quoted-char = %x0-5B ; omit \
/ %xE000-10FFFF

unquoted = unquoted-start *name-char
unquoted-start = name-start / DIGIT / "."
/ %xB7 / %x300-36F / %x203F-2040
unquoted-start = ALPHA / DIGIT / "." / "_"
/ %xB7 / %xC0-D6 / %xD8-F6 / %xF8-37D
/ %x37F-1FFF / %x200C-200D / %x203F-2040
/ %x2070-218F / %x2C00-2FEF / %x3001-D7FF
/ %xF900-FDCF / %xFDF0-FFFD / %x10000-EFFFF
```

### Names

A **_<dfn>name</dfn>_** is an identifier for a _variable_ (prefixed with `$`),
for a _function_ (prefixed with `:`, `+` or `-`),
or for an _option_ (these have no prefix).
The namespace for _names_ is based on XML's [Name](https://www.w3.org/TR/xml/#NT-Name),
with the restriction that it MUST NOT start with `:`,
as that would conflict with the _function_ start character.
Otherwise, the set of characters allowed in names is large.
The namespace for _name_ matches XML's [Name](https://www.w3.org/TR/xml/#NT-Name).

As `:` is also used as the start sigil of _function_,
using a _name_ with it as a first character is NOT RECOMMENDED.
Comment on lines +634 to +637
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I disagree with this. We have namespacing in another PR just now and there's a reasonable solution: instead of XML Name use XML-Name's NCName as the basis. The definition of NCName is exactly "Name minus the : character"

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Why should there be such an unnecessarily complex overlap between variable/function/option names and unquoted literals? If the function sigil were just replaced with something that does not appear in XML NameChar then the names could be exactly described by XML Name and the unquoted literals by either 1*name-char (i.e., XML Nmtoken) or by 1*(name-char / "+" / …), in either case forming a strict superset rather than a near-superset to exclude artificially-induced ambiguity w.r.t. colons.


```abnf
variable = "$" name
function = (":" / "+" / "-") name

name = name-start *name-char
name-start = ALPHA / "_"
name-start = ALPHA / ":" / "_"
/ %xC0-D6 / %xD8-F6 / %xF8-2FF
/ %x370-37D / %x37F-1FFF / %x200C-200D
/ %x2070-218F / %x2C00-2FEF / %x3001-D7FF
/ %xF900-FDCF / %xFDF0-FFFD / %x10000-EFFFF
name-char = name-start / DIGIT / "-" / "." / ":"
name-char = name-start / DIGIT / "-" / "."
/ %xB7 / %x300-36F / %x203F-2040
```

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