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Re: [css3-values] unitless zero lengths inside 'calc()'

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Wed, 29 Dec 2010 09:56:00 -0800
Message-ID: <AANLkTi=eSDm6Wvy-7Gm9ioecmDRFcG81UQcaYbr_zvp+@mail.gmail.com>
To: "L. David Baron" <dbaron@dbaron.org>
Cc: www-style@w3.org
On Wed, Dec 29, 2010 at 9:41 AM, L. David Baron <dbaron@dbaron.org> wrote:
> calc() expressions, defined in
> http://dev.w3.org/csswg/css3-values/#the-calc-min-and-max-functions ,
> do not allow unitless zero to be treated as a length, since the spec
> says:
>  # The context of the expression imposes a target type, which is
>  # one of length, frequency, angle, time, or number. NUMBER tokens
>  # are of type number. DIMENSION tokens have types of their units
>  # (‘cm’ is length, ‘deg’ is angle etc.); any DIMENSION whose type
>  # does not match the target type is not allowed and must be a
>  # parse error.
> I think this is a good thing; the only use cases for zero lengths
> that I can think of are for the output of tools that might be
> generating nonzero lengths, and in such cases the tool would
> presumably be generating the unit anyway.
> However, since this isn't explicitly stated, and it might trip up
> authors or implementors, I think it would be good to add a note
> (near the text above) that this means that '0' is never a dimension
> inside calc(), even though it is allowed to be a length outside of a
> calc() expression.

Agreed on all points.  0 lengths aren't very useful in calc(),
machines generating them will probably put a unit in anyway, and we
should have an explicit note in the spec so people don't make
assumptions based on how the grammar works elsewhere in the language.

Received on Wednesday, 29 December 2010 17:56:52 UTC

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