W3C home > Mailing lists > Public > www-svg@w3.org > July 2015

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

From: Dirk Schulze <dschulze@adobe.com>
Date: Mon, 27 Jul 2015 08:10:12 +0000
To: www-style list <www-style@w3.org>, www-svg <www-svg@w3.org>
Message-ID: <D3EA68BE-0B85-40AB-B17C-A170FB3EAAB7@adobe.com>
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).

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.


For backward compatibility (WebKit and Blink support the old property values for SVG text) I would like to suggest to make them deprecated but mandatory. All values must be mapped as suggested by the spec currently.

For tool creators and libraries it is just not possible to address browsers with full CSS3 Writing Mode support, browsers based on current WebKit and Blink as well as older (often proprietary) SVG viewers at the same time.

Greetings,
Dirk

[1] https://drafts.csswg.org/css-writing-modes-3/#svg-writing-mode
Received on Monday, 27 July 2015 08:10:45 UTC

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