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Re: [css-writing-modes] 'writing-mode' and deprecated SVG values

From: fantasai <fantasai.lists@inkedblade.net>
Date: Wed, 26 Aug 2015 03:52:55 +0200
To: Dirk Schulze <dschulze@adobe.com>, www-style list <www-style@w3.org>, www-svg <www-svg@w3.org>
Message-ID: <55DD1BF7.1060702@inkedblade.net>
Forgot to CC SVG... also correction to the last item.

On 07/27/2015 04:10 AM, Dirk Schulze wrote:
> Hi,
>
> The CSS3 Writing Mode spec currently says:
>
> "These values are deprecated in any context except SVG1 documents. Implementations
> that wish to support these values in the context of CSS must treat them as follows”
> <Table of mapping old value to new values>[1].
>
> I have two issues with this:
>
> 1) Presentation attributes:
>
> In CSS you can usually do things like
>
> .class {
>     writing-mode: tb; /*old SVG values*/
>     writing-mode: vertical-lr; /*new CSS values*/
> }
>
> For SVG, this would add support for the old values and the new values.
> However, this is not a possibility in XML with presentation attributes:
>
>     <text writing-mode=“tr” writing-mode="vertical-lr”>..</text>
>
> would cause an XML parsing error. A attribute can not be declared twice.
> From Adobe products we know that presentation attribute export is still very
> popular and you find multiple JS libraries (like SVGO) which transform
> properties to attributes (even by default).

I think it would be very easy for a UA to add a ua.css mapping of
   svg|*[writing-mode=tb] { writing-mode: vertical-rl; }
to support such content, now and into the future. And I'm happy to add
a note to Writing Modes clarifying that although these values are
deprecated in general, content that uses the presentation attributes
should continue to use the old forms as long as there are UAs out there
that need them.

> 2) Implementation complexity
>
> The spec currently just allows the values for SVG documents. It can not be
> determined at parse time if a property inheriting element will be in an
> HTML or an SVG context. (See inline SVG.) So the first sentence is actually
> hard to implement since the parser needs to accept the SVG values initially
> and then needs to verify if they apply to a certain element or not. A valid
> parsing is prohibited at the same time by the spec though.

The spec does not require any sort of context-dependent parsing. It says
"These values are deprecated in any context except SVG1 documents." which
means "Don't use them anywhere except SVG1 documents." Deprecated features
must still be supported.

Please let me know if this resolves your concern.

~fantasai
Received on Wednesday, 26 August 2015 01:53:27 UTC

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