[HarfBuzz] U+1A55 TAI THAM MEDIAL RA Reordering in HarfBuzz?

[Ed Trager]

Hi, Behdad and List Members,

In Firefox 20.0 on Mac OS X and in Firefox 18.0.2 on Ubuntu, I see that the
five PREFIXED TAI THAM DEPENDENT VOWEL SIGNS  U+1A6E, 1A6F, 1A70, 1A71,
1A72 are correctly reordered and the spacing/kerning after reordering is
also correct.

HOWEVER, U+1A55 TAI THAM MEDIAL RA is *NOT* being reordered in these two
versions of Firefox ...  May I kindly ask WHY IS THAT ?

Surely FF 18.0.2 on Ubuntu is using HarfBuzz, yes?  I'm not sure about FF
20.0 on Mac OS X -- also using HarfBuzz or not ?

On a related note, I see that Google Chrome Version 26.0.1410.65 on Mac OS
X attempts to reorder both the PREFIXED DEP VOWEL SIGNS and MEDIAL RA but
the spacing is all wrong and all of the reordered glyphs are just
left-aligned to the base consonant instead of actually prefixed.  I'm not
sure which layout engine is Chrome using on OS X?

Best - Ed

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