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

From: Dirk Schulze <dschulze@adobe.com>
Date: Wed, 26 Aug 2015 08:18:15 +0000
To: fantasai <fantasai.lists@inkedblade.net>
CC: www-style list <www-style@w3.org>, www-svg <www-svg@w3.org>
Message-ID: <4B187B55-CB5B-4AB3-9DC9-C18B35E371EC@adobe.com>

> On Aug 26, 2015, at 3:52 AM, fantasai <fantasai.lists@inkedblade.net> wrote:
> 
> 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.

All browsers I know have a SVG specific UA style rule with @namespace "http://www.w3.org/2000/svg”; So it could be generalized to elements in this namespace. 

> 
>> 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.

The last sentence would rule out the usage of the deprecated values in inline SVG (SVG content in a HTML document). Or do I misinterpret it?

Greetings,
Dirk

> 
> Please let me know if this resolves your concern.
> 
> ~fantasai
> 

Received on Wednesday, 26 August 2015 08:18:51 UTC

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