[HarfBuzz] Some questions about scripts and languages

[Richard Wordingham]

On Sun, 6 Dec 2015 09:07:58 +0530
Deepak Jois <deepak.jois at gmail.com> wrote:

> On Sat, Dec 5, 2015 at 8:22 PM, Khaled Hosny <khaledhosny at eglug.org>
> wrote:
> >> 2. Is there a canonical list of languages that are defined in any
> >> font standard? Can/does Harfbuzz validate against them? The answer
> >> seems no from a cursory look at the code.
> >
> > https://www.microsoft.com/typography/otspec/languagetags.htm
> 
> If there is such a list, why doesn’t Harfbuzz validate the language
> tag, like it does for script. I checked and I was able to pass in an
> arbitrary string as a language.

It is pretty much the same argument as for not validating characters.
The list of languages with tags is large and keeps on growing, and
coverage is far from complete.  Additionally, I don't think there is
such a thing as a private use language tag.

A language tag specifies which lookup tables in a font are to be used
(more precisely, which variants of the features).  A script tag
frequently invokes specific shaping functionality, defined in the
renderer.

Richard.