Re: WebVTT feedback

On Tue, Dec 20, 2011 at 7:25 PM, David Singer <singer@apple.com> wrote:
> > With or without language information, font switching is needed. I
assume that you don't mean that Chinese text in something labeled as
English shouldn't be rendered at all, so how should the font for each
character be picked?
>
> I'm not sure I get the question.  I'm suggesting that if you want correct
behavior, I would expect to see a VTT file labelled as 'generally
lang=en-US' but this <span> has lang=zh.  (I'm using short language codes
here, but full BCP 47 codes might be better).

The problem is that tagging a span lang=en doesn't prevent including CJK
codepoints.  The UA still has to choose which language glyphs to use in
that case, so merely providing a default @lang value, or requiring that one
be provided, doesn't solve the interop problem.

> In the absence of font tagging, I would assume that the UA has a set of
fonts that are suitable for the intersections of Unicode characters and
languages used.  Does that not work?

It doesn't work in an interoperable way, since every browser has its own
rules for this choice.  Worse, some of the rules depend on the user's
configuration.

> If the question is, what happens when the author fails to tag his content
with the languages, well, he may not get the expected result.

The answer should be that you get a predictable, well-defined result, even
if it's not what the user expected.  It would be nice to get there, or
closer to it, but WebVTT doesn't seem like the place to solve it.

One possible approach--just to brainstorm a little--would be for HTML to
define an attribute "predictableLanguages" (can't think of a good name).
If set, glyph selection would be switched to a new, well-defined,
interoperable mechanism.

WebVTT would simply set this attribute on generated DOM nodes Importantly,
the solution would be in the right place--HTML, in the regular layout
engine--not a WebVTT-specific special case.

Not great, but an idea.  It's basically an escape hatch if all attempts to
standardize glyph selection are going to fail due to legacy content.  I
don't know if it's too early to give up on that.  (Of course, actually
defining language selection properly would still be a significant task.)

--
Glenn Maynard