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Re: ISSUE-299: Cluster matching 1b

From: John Daggett <jdaggett@mozilla.com>
Date: Thu, 12 Sep 2013 20:59:31 -0700 (PDT)
To: Richard Ishida <ishida@w3.org>
Cc: W3C Style <www-style@w3.org>, www International <www-international@w3.org>
Message-ID: <1045309777.7978012.1379044771010.JavaMail.zimbra@mozilla.com>

Richard Ishida wrote:

> 5.3. Cluster matching
> http://www.w3.org/TR/2013/WD-css-fonts-3-20130711/#cluster-matching
> 
> In the numbered list, what should follow if 1b holds true?

Um, you select that font and great joy ensues? ;)  That's the goal of
both standard font matching and the font matching for clusters. Steps
(2) and (3) are prefaced with "if no font was found..." so I don't see
any ambiguity if that's what you're thinking there's something
ambiguous here.

> "If a sequence of multiple codepoints is canonically equivalent to a 
> single character and the font supports that character, select this font 
> for the sequence."
> 
> Is this implying (though not stating, note), that the text should be 
> normalized so that the glyph for the canonically equivalent character 
> can be used? (I'm not sure that's a good idea.)

The words here were carefully selected to mean exactly what is
written.  The text is not normalized because that would mean
normalization of single, non-cluster codepoints. This would make it
impossible to display CJK compatibility codepoints correctly since
these are transformed under canonical normalization (despite their
"compatibility" label).  Japanese names can include these characters.

> Or is the meaning that if the font has a glyph for the precomposed 
> character that is canonically equivalent to the sequence of characters, 
> then that glyph should be used (without changing the sequence of 
> characters itself). That would seem to make more sense.

Yes, that's exactly what section 5.2 is addressing.  For a *sequence*
of codepoints, a glyph for a canonically equivalent character can be
used.  This is, in fact, already the norm for most modern layout
engines.

> Otherwise, it's not clear why you would select the font for this sequence.

??? Sorry, I don't quite get what you're saying here.

Regards,

John Daggett
Received on Friday, 13 September 2013 03:59:58 UTC

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