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Re: [css3-writing-modes] Summary of Tr in UTR#50 and 'text-orientation' discussions

From: John Daggett <jdaggett@mozilla.com>
Date: Wed, 9 Oct 2013 10:09:23 -0700 (PDT)
To: Rossen Atanassov <Rossen.Atanassov@microsoft.com>
Cc: Koji Ishii <kojiishi@gluesoft.co.jp>, www-style@w3.org, "CJK discussion (public-i18n-cjk@w3.org)" <public-i18n-cjk@w3.org>
Message-ID: <668404516.2245428.1381338563440.JavaMail.zimbra@mozilla.com>

Rossen Atanassov wrote:

>> We resolved two years ago to base orientation *normatively* on a
>> clear, well-defined orientation character property.  Through many
>> twists and turns, we've basically got something that works, is
>> fairly clear, and for the most part reflects common practice. 
>> There's just one crumb of "optional" behavior for "Tr" codepoints
>> that doesn't makes sense for authors or implementations.  I suggest
>> that rather than giving up on normatively defining default
>> orientation that we simply purge the optional behavior and move on.
> 
> Removing the entire section of 5.1.1 will contradict the above
> resolution - agreed. However, if we were to drop the second part of
> that section should give us defined behavior for character
> orientation while leaving Tr to Unicode. This is the sentence I
> propose we remove.
> 
> "For Tr characters, which are intended to be either transformed or
> rotated sideways, the UA may assume that appropriate glyphs for
> upright typesetting are given in the font and render them upright;
> alternately it may check for such glyphs first, and fall back to
> typesetting them sideways if the appropriate glyphs are missing."

This would work as long as Tr is explicitly included in the previous
sentence.

Current wording:

# [UTR50] defines the Vertical_Orientation property for the default
# character orientation of mixed-orientation vertical text. When
# text-orientation is mixed, the UA must render a character upright if
# its orientation property is U or Tu; or typeset it sideways (90°
# clockwise from horizontal) if its orientation property is R. For Tr
# characters, which are intended to be either transformed or rotated
# sideways, the UA may assume that appropriate glyphs for upright
# typesetting are given in the font and render them upright;
# alternately it may check for such glyphs first, and fall back to
# typesetting them sideways if the appropriate glyphs are missing. 

Trimmed version:

# [UTR50] defines the Vertical_Orientation property for the default
# character orientation of mixed-orientation vertical text. When
# text-orientation is mixed, the UA must render a character upright if
# its orientation property is U, Tu or Tr; or typeset it sideways (90°
# clockwise from horizontal) if its orientation property is R.

You need to include Tr here so that it's clear which way Tr is handled
(i.e. upright or sideways).  The handling of the upright and sideways
categories is then detailed in section 5.1.2.  Omitting it from this
sentence leaves the CSS handling undefined.  I don't think it's
sufficient to point to UTR50 to indicate what the behavior is.  UTR50
describes a character property, it does not define normative behavior
handling OpenType fonts.

Regards,

John Daggett
Received on Wednesday, 9 October 2013 17:09:53 UTC

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