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RE: [css21][css3][svg] SVG and unit-less length values

From: Sylvain Galineau <sylvaing@microsoft.com>
Date: Wed, 7 Jul 2010 15:02:00 +0000
To: Boris Zbarsky <bzbarsky@MIT.EDU>
CC: "www-style@w3.org list" <www-style@w3.org>, "public-fx@w3.org" <public-fx@w3.org>
Message-ID: <045A765940533D4CA4933A4A7E32597E214FC358@TK5EX14MBXC120.redmond.corp.microsoft.com>
> From: Boris Zbarsky [mailto:bzbarsky@MIT.EDU]
> Sent: Wednesday, July 07, 2010 7:48 AM
> To: Sylvain Galineau
> Cc: www-style@w3.org list; public-fx@w3.org
> Subject: Re: [css21][css3][svg] SVG and unit-less length values
> 
> On 7/7/10 7:03 AM, Sylvain Galineau wrote:
> > This means the validity of a length property value depends on the
> property and/or the type of node it applies to.
> 
> It does not depend on the type of node it applies to, in fact.
> 
> > [3] http://www.w3.org/TR/SVG/types.html#DataTypeLength
> 
> As the text at this link clearly says:
> 
>    For properties defined in CSS2 [CSS2], a length unit identifier
>    must be provided. For length values in SVG-specific properties
>    and their corresponding presentation attributes, the length unit
>    identifier is optional.
> 
> Now this leaves a loophole the size of a truck for properties not in
> CSS2 but presend in CSS2.1 or CSS3...  But that's pretty easy to fix.

Pretty easy is good. Let's just say bringing up this issue internally
and externally has caused much surprise and some level of dismay. Authors,
in particular, find this confusing. My main goal here is to try and reduce
that surprise. I also would like to be very clear on where this exception
applies; I don't think the prose above is quite there i.e. does SVG-specific
mean an SVG property applying to an SVG node so that it would be ignored and
thus wouldn't show in the OM of a non-SVG node ?

> 
> In any case, it doesn't seem like changes are needed here for
> line-height, for example.  Though note the recent discussion about how
> this stuff is supposed to interact with SMIL type="CSS" animations on
> www-svg.
> 
>  > The CSSWG must of course keep this in mind when defining new
>  > properties that are intended to apply to SVG documents.
> 
> Only insofar as we need to avoid name collisions with existing
> properties that the SVG specification defines and which it therefore
> requires to have the unitless length behavior, no?

Not just that. If a CSS3 or 4 module defines a new feature that is
intended to also apply to SVG documents - e.g. transitions - it must make
sure to not use the line-height or columns property pattern where both
numbers and lengths can be set as value.
Received on Wednesday, 7 July 2010 15:02:36 GMT

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