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Re: '-vnd' identifiers

From: Bert Bos <bert@w3.org>
Date: Tue, 29 Jan 2002 19:03:17 +0100
Message-ID: <15446.58341.46058.337769@jfouffa.inria.fr>
To: "'www-style@w3.org'" <www-style@w3.org>
Mats Tedenvall writes:
> Hi,
> I heard that future versions of CSS might support vendor-specific extensions
> by allowing identifiers to begin with '-'. That would allow vendor-specific
> properties such as -wap-input-format (WAP Forum extension) or
> -xyz-inner-border-color (xyz company extension).
> I wonder how that could be syntactical possible, since it would then be
> impossible for a tokenizer to separate negative numbers from identifiers.
> For example, is '-123' a negative number or is it an identifier?

Yes, this has been an unwritten convention for a while.

In April last year, we were on the point of publishing a draft
describing it, but then we reorganized things a bit and decided that
this convention was not a CSS module on its own, but really just a
section in the Syntax module. The Syntax module is slowly getting ripe
for publication, but is taking longer than expected :-(

An identifier indeed cannot start with a dash. That is fine, because
it guarantees that the official CSS will never contain such
identifiers. If some implementation has an extension, it just has to
extend the parser a bit as well. In essence, it will have to accept
the pair of tokens "-" + identifier as a "proprietary identifier."
(But note that '-123' is not a valid example, because '123' starts
with a digit and is therefore a number, not an identifier.)

However, some implementers complained that re-combining the minus and
the identifier made things too hard for them, because they couldn't
use an off-the-shelf CSS parser. Thus the latest plan is to also allow
proprietary identifiers that start with an underscore ('_vnd_foo').
The CSS WG thereby promises to not use underscores at the start for
any official property. (That is not very hard, because CSS has always
carefully avoided underscores anywhere, because of their geeky look,
that might scare users.)

Of course, publishing the convention doesn't mean that we think
proprietary extensions are OK in general, just that there may be cases
(UA style sheets, experiments, etc.) where they are needed. This
convention can make their use a little bit easier without harm to CSS.



Bert
-- 
  Bert Bos                                ( W 3 C ) http://www.w3.org/
  http://www.w3.org/people/bos/                              W3C/INRIA
  bert@w3.org                             2004 Rt des Lucioles / BP 93
  +33 (0)4 92 38 76 92            06902 Sophia Antipolis Cedex, France
Received on Tuesday, 29 January 2002 13:03:18 GMT

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