[HarfBuzz] Support for Stylistic Sets

[Richard Wordingham]

On Sat, 14 Sep 2019 18:59:56 +0300
Eli Zaretskii <eliz at gnu.org> wrote:

> The next question is how to know whether a given hb_font_t supports a
> given feature?

I think it's safe to specify the use of unsupported features, in which
case this is a luxury feature.  One complication is that features are
provided by a font on a (per script) per language basis.

For example, my Da Lekh font provides feature ss19 for the default
language, but not for Lao, Tai Lü or 'Shan'. In this font, Feature
ss19 means apply Lao style, and that is applied automatically if the
font is told it is being used for Lao. It would be a bit off to tag
aerated Pali text as Lao just to get a Lao style. Aerated Pali has
different line-breaking rules to Lao, which is written without visible
word separation.

Richard.