[css-variables][css-conditional] allowing a white space only variable value

[svgeesus]

from https://lists.w3.org/Archives/Public/www-style/2013Aug/0520.html by @heycam

I assume we want:

@supports (var-a: ) { }

to succeed, since "var-a: " is a valid declaration. However,
css-conditional-3 has:

  supports_declaration_condition
    : '(' S* declaration ')'
    ;

with "declaration" linking to CSS 2.1, where it is defined as:

  declaration : property S* ':' S* value;
  value       : [ any | block | ATKEYWORD S* ]+;
  any         : [ IDENT | NUMBER | PERCENTAGE | DIMENSION | STRING
                | DELIM | URI | HASH | UNICODE-RANGE | INCLUDES
                | DASHMATCH | ':' | FUNCTION S* [any|unused]* ')'
                | '(' S* [any|unused]* ')' | '[' S* [any|unused]* ']'
                ] S*;

This doesn't allow for a property value that consists only of white space.

On the other hand,
http://dev.w3.org/csswg/css-syntax/#consume-a-declaration seems to allow
a declaration to be parsed that has no tokens at all after the ':'. I
guess that's OK as css-variables then defines that no tokens after the
':' is invalid?

[svgeesus]

from https://lists.w3.org/Archives/Public/www-style/2013Aug/0540.html by @tabatkins

CSS Conditional's references to the 2.1 grammar are there only because
Syntax wasn't yet even a WD. It, and anything else that needs
explicit token-grammar stuff, should switch over to Syntax in the
nearish future.

Yes, it's okay that Syntax technically accepts "var-foo:;" but it's
invalid per Variables - it's just a property grammar being more
specific than the generic grammar.

[svgeesus]

@heycam @tabatkins is this one closed? Sounds like Needs Edits on conditional-3 at least (which may subsequently have been done, idk)

[tabatkins]

Insofar as Conditional is now specified in terms of Syntax, yes.