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Re: [1.2T-LC] Lack of BIDI 'direction' (ISSUE-2058 ACTION-2201)

From: Doug Schepers <schepers@w3.org>
Date: Thu, 18 Sep 2008 14:19:10 -0400
Message-ID: <48D29B9E.3000304@w3.org>
To: fantasai <fantasai.lists@inkedblade.net>, www-svg <www-svg@w3.org>

Hi, fantasai-

> fantasai wrote (on 9/17/08 1:51 PM):
>> There's discussion in http://www.w3.org/TR/SVGMobile12/text.html about
>> bidirectional text, but there is no definition for a 'direction' property
>> that I can find, nor any mention of any substitute for it (such as a 'dir'
>> attribute).
>> This is a problem because the Unicode bidirectional algorithm needs a
>> base direction for each "paragraph" that it operates on. For plain text
>> it guesses based on the first character in the text, but this is not
>> always accurate. Applying this rule to SVG Tiny would be incompatible
>> with an implementation that supported SVG Tiny plus the 'direction'
>> property because 'direction' defaults to 'ltr', not to 'guess a direction'.
>> The lack of a 'direction' affects both bidi reordering and other properties
>> like 'text-align', whose values' behavior depends on 'direction'.
>> I therefore strongly recommend that SVG Tiny include the 'direction'
>> property.

The SVG WG discussed this issue, and we agree that your issue makes sense.

SVG1.1 Full does support the 'direction' property. [1] The challenge for
SVG 1.2 Tiny user agents is that they frequently rely upon the
underlying platform's text rendering engine for the directionality of
text.  Even when the underlying platform does support right-to-left
text, it doesn't always allow the user agent to dictate when the
directionality is switched; for example, the UA might not be able to
make English text go right-to-left.

We are reluctant to include optional features in SVG.  We are more
comfortable with making conditional features.  While we are looking more
into this issue, we have a tentative proposal we'd like your feedback on.

Would the CSS WG be comfortable if we introduced the 'direction'
property, but included the proviso that it's platform-dependent?

As a side note, since 'direction' has no effect unless 'unicode-bidi' is
'embed' or 'bidi-override', we would also have to include that property.
 (Just curious, why is this dependency here in CSS?  Why can 'direction'
not apply no matter what the circumstances?  Unless there is a clear and
common use case when 'direction' should not apply directly, it would
seem easier and more intuitive for authors.)

[1] http://www.w3.org/TR/SVG11/text.html#DirectionProperty

-Doug Schepers, on behalf of the SVG WG
Received on Thursday, 18 September 2008 18:19:46 UTC

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