Compatibility decomposition for Hebrew and Greek final letters

Julian Bradfield jcb+unicode at
Thu Feb 19 05:47:24 CST 2015

On 2015-02-19, Eli Zaretskii <eliz at> wrote:
> Does anyone know why does the UCD define compatibility decompositions
> for Arabic initial, medial, and final forms, but doesn't do the same
> for Hebrew final letters, like U+05DD HEBREW LETTER FINAL MEM?  Or for
> that matter, for U+03C2 GREEK SMALL LETTER FINAL SIGMA?

As far as I understand it:
In Arabic, the variant of a letter is determined entirely by its
position, so there is no compelling need to represent the forms separately
(as characters rather than glyphs) save for the existence of legacy
standards (and if there is, you can use the ZWJ/ZWNJ hacks). Thus the
forms would not have been encoded but for the legacy standards.
Whereas in Hebrew, non-final forms appear finally in certain contexts
in normal text; and in Greek, while Greek text may have a determinate
choice between σ and ς, there are many contexts where the two symbols
are distinguished (not least maths).

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