[HarfBuzz] Handling OpenType layout across itemisation boundaries

[Khaled Hosny]

While reading page 13 of John Hudson’s IUC39 presentation [1], I was
wondering if HarfBuzz can handle script, language and direction
properties the same way it handles optional features; i.e. instead of
sending HarfBuzz buffers that has a single script, language and
direction, one sends a single buffer for the whole paragraph with
arrays of script etc. ranges similar to hb_feature_t ranges and let
HarfBuzz do its magic on it, allowing for any cross boundary lookups to
be applied as the required context will not be lost.

WDYT?

1. http://tiro.com/John/Hudson_IUC39_Beyond_Shaping.pdf