RE: [css3-fonts] font selection for Unicode Variation Selector

> The question is not difficulty, I don't think it's the right
> behavior to require font fallback for UVS selectors.
> It doesn't make sense to me the way the Unicode spec is
> written, it doesn't make sense from given the way other
> font variant features work and it doesn't make sense to
> me from a performance perspective.

First, there are two perspective; "should", and "technically feasible", and I understand both are important. What you mentioned first is about "should", and performance etc. are the later. I would like to focus on "should" first, because you mentioned you don't think it's the right behavior. If we could agree on we "should", we could then discuss if it's feasible, or if there were any compromises to make it. If we agree on we "should NOT", then the discussion is over.

UVS is different from font variant features. If they were the same or even similar, they wouldn't implement it in Unicode. Rather, they should be done in OpenType.

One Unicode expert I know suggested that the "default ignorable" wording in Unicode is the philosophy for collation/comparison/sorting etc., rather than the display. If it were about styling, it won't make UVS and should be done as OpenType feature as you said. They were done in UVS because the glyph is different, but we want to ignore the difference on collation/comparison/sorting etc.

There are some glyphs that have pretty significant differences from its base glyph in IVS (some samples are marked in pink at this page[1]).

Also I just knew that it's not only about ideographic (and therefore including www-international). A set of variants is defined at Unicode as STANDARDIZED VARIANTS[2] and you see some variants are significantly different.

He also raised another interesting question; if font B has "a" and Umlaut[3] while font A has only "a", and source text is
  U+0061 LATIN SMALL LETTER A
  U+0308 COMBINING DIAERESIS
Would CSS render the glyph using font A or B? If it uses font A, the Umlaut will not be rendered.

He suggested that UVS is closer to the combining marks rather than OpenType font variant features.

I'm still collecting information about actual implementation of IVS as of now and will get back here once I got them. but I hope you at least understand that UVS and OpenType font variants are two different features, although the two shares the word "variants".


Regards,
Koji

[1] http://kanji-database.sourceforge.net/ucs/ivd.html

[2] http://unicode.org/Public/UNIDATA/StandardizedVariants.html

[3] http://en.wikipedia.org/wiki/Germanic_umlaut


-----Original Message-----
From: John Daggett [mailto:jdaggett@mozilla.com] 
Sent: Monday, February 21, 2011 5:26 PM
To: Koji Ishii
Cc: www-style@w3.org; John Hudson; CJK discussion (public-i18n-cjk@w3.org)
Subject: Re: [css3-fonts] font selection for Unicode Variation Selector

Koji Ishii wrote:

> I understand this is probably technically difficult, and I also 
> understand that current IVS spec allows not doing this as John Hudson 
> pointed out. But I wish you aware of that people's expectation is 
> different.

The question is not difficulty, I don't think it's the right behavior to require font fallback for UVS selectors.  It doesn't make sense to me the way the Unicode spec is written, it doesn't make sense from given the way other font variant features work and it doesn't make sense to me from a performance perspective.

If you think there's an actual use case that warrants fallback to find a font that supports a particular UVS, please describe it in detail.

Regards,

John Daggett

Received on Monday, 21 February 2011 12:19:13 UTC