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

From: John Daggett <jdaggett@mozilla.com>
Date: Mon, 14 Oct 2013 21:14:25 -0700 (PDT)
To: MURATA Makoto <eb2m-mrt@asahi-net.or.jp>
Cc: www-style@w3.org, "CJK discussion (public-i18n-cjk@w3.org)" <public-i18n-cjk@w3.org>
Message-ID: <629150087.3009769.1381810465133.JavaMail.zimbra@mozilla.com>

Makoto Murata wrote:

> I have been wondering whether this debate is about factual
> matters or subjective value judgement.  Here is my (rough)
> understanding of John's argument.
> (1) Since implementation costs are heavy, even optional
>     fallback should be disallowed.

No, my point is that it's simply *unnecessary* in the context of
OpenType fonts that supply vertical alternates for nearly all Tr
codepoints.  This is based on looking at actual fonts rather than
abstract notions of whether fallback is beneficial or not.  The only
thing that's subjective is whether one takes the viewpoint that
this fallback is beneficial even if it only affects a handful of
codepoints in practice.

> (2) Fallback lead to negative side effects.

> (3) Optional fallback confuse authors.

Optional fallback leads to differences in behavior across user agents
with the same fonts.  For U or R codepoints, when the default
orientation is not what an author desires, they'll see that it isn't
correct and use markup to adjust it.  They won't always see this for
Tr codepoints because the behavior will vary
across user agents.  Having incorrect behavior for a small set of 
codepoints is not beneficial to users; explicit markup assures that
it's correct.

In short, existing practice is that the transformation required for Tu
and Tr codepoints is handled via an OpenType feature.  For situations
where a font is missing vertical alternates for Tu and Tr codepoints,
a better made font can be used or, in the case of Tr codepoints,
explicit markup can be used.

Down the road, as fonts standardize the set of alternates they provide
based on UTR50, there will be no need for this fallback feature and
this entire discussion will be moot.


John Daggett
Received on Tuesday, 15 October 2013 04:14:52 UTC

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