[HarfBuzz] vertical text for RTL scripts?

[Phil M Perry]

(my first digest copy arrived moments after posting my previous update)

Richard,

"Top To Bottom" means that the characters (glyphs) are upright (top 
uppermost), as they would be written horizontally, but stacked in a 
column one-at-a-time and reading from the top to the bottom. BTT (Bottom 
To Top) would be the same, except reading from bottom to top.

I noted that with a cursive script such as Arabic, when written 
horizontally, connects letters (also there are a lot of ligatures). When 
written vertically, the individual "standalone" forms of letters are 
used, so no connections. I would presume that Mongolian and Phags-pa 
would do something similar. Latin text (and CJK) are normally 
non-cursive (unconnected), as you note.

Phil