It's been more than a year since I introduced myself to this forum, so I must say again that I'm not a font designer, but a programmer that is interested in fonts, more specifically in open type fonts. I've been playing with the arial.ttf font in the last few days, and by parsing the file I was surprised with some apparent inconsistencies, as I summarized in the attached file.
The figure on this file is very simple. They represent just a small number (3) of the ligatures substitutions extant in the "ccmp" feature, for default language system, for the "arab" script, on the font arial.ttf .
The hexadecimal numbers on the right are glyph ID's associated with the Unicode numbers for each glyph on the left. The leftmost glyph is the one that should replace the two on the right.
The problem that I see with these ligatures is that, when I type them in MS Word, nothing happens, i.e., no replacement can be seen for the two glyphs, with the one on the left.
I also would appreciate to learn how to insert a figure in this box, for I tried hard to no avail.
Thanks for your patience.