bug#20537: 25.0.50; `compose-string-internal` does not work properly on OSX.

[Keith David Bershatsky <esq@lawlist.com>]

I believe the answer to the first question is available from the `(frame-parameters)` -- i.e., (font-backend mac-ct ns).

Some preliminary Googling relating to Emacs and "complex text layout" pops up a few results that mention Emacs built using Macports.  I haven't tried using that particular version of Emacs -- the Emacs versions that I use are built from scratch using `--with-ns` or downloaded from http://emacsformacosx.com/

I'll continue to do some more Googling to see if I can be of better assistance.

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At Sat, 09 May 2015 21:52:57 +0300,
Eli Zaretskii wrote:
> 
* * *
> Character composition depends on the font driver doing TRT.  Which
> font driver does your Emacs use, and does that driver support complex
> text layout?