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Re: [css-values] Relaxing <custom-ident> restrictions when unambiguous

From: Simon Sapin <simon.sapin@exyr.org>
Date: Thu, 06 Mar 2014 11:57:38 +0000
Message-ID: <531862B2.50507@exyr.org>
To: fantasai <fantasai.lists@inkedblade.net>, www-style@w3.org, "L. David Baron" <dbaron@dbaron.org>
On 06/03/2014 04:29, fantasai wrote:
> On 03/04/2014 03:22 PM, Simon Sapin wrote:
>> Hi,
>> CSS Values and Units currently defines:
>> http://dev.w3.org/csswg/css-values/#custom-idents
>>> Some properties accept arbitrary author-defined identifiers as a
>>> component value. This generic data type is denoted by <custom-ident>,
>>> and represents any valid CSS identifier that does not otherwise
>>> appear as a pre-defined keyword in that property's value definition.
>>> [...]
>>> The CSS-wide keywords are not valid <custom-ident>s. The ‘default’
>>> keyword is reserved and is also not a valid <custom-ident>s.
>> This is more restrictive than it needs to be.
> OK, I've updated the spec:
>     http://dev.w3.org/csswg/css-values-3/#custom-idents
> New text:
>     # Specifications using ‘<custom-ident>’ should specify clearly
>     # what other keywords are excluded from <custom-ident>—
>     # for example by saying that any pre-defined keywords
>     # in that property's value definition are excluded.
>     # As a general rule,an identifier that could be interpreted
>     # as a pre-defined keyword in any position or multiplication
>     # of the <custom-ident> component value is excluded,
>     # and is invalid as a <custom-ident> matching to that component value
>     # even in positions where its use would be technically unambiguous.
>     # For example, if a keyword could be misparsed when specified
>     # as the first item of a ‘<custom-ident>+’ list, it is invalid
>     # when specified in any position in that list.
> Let me know if that seems good.

The paragraph before the one you quoted is:

> The CSS-wide keywords are not valid <custom-ident>s. The ‘default’
> keyword is reserved and is also not a valid <custom-ident>.

Do we want to exclude these even when they’re not ambiguous? For 
example, <custom-ident> in CSS Grid’s <line-names> is completely 
unambiguous thanks to the parens.

<'font-family'> is currently not defined with <custom-ident>. But if it 
were, it would be unambiguous when in the 'font' shorthand because of 
the mandatory <'font-size'> that separate it from other keywords.

Simon Sapin
Received on Thursday, 6 March 2014 11:58:13 UTC

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