[HarfBuzz] vertical text for RTL scripts?

[Phil M Perry]

OK, after digesting what Eli, Jonathan, and Richard had to say (thank 
you all for your feedback), I think you're in agreement that normally 
RTL scripts such as Hebrew should be rendered vertically Top To Bottom 
(first input character output at the top, and growing downwards, just as 
with English). I erred in stating "last input, first read", as pointed 
out (self-administered dope slap goes here). It sounds like my TTBHebrew 
example in HarfBuzz.pdf (did anyone look at it?) is correct output, and 
embedded normally LTR (e.g., English) text should not be reversed from 
the order used by the normally bidirectional/RTL text (continue to write 
TTB).

Regarding Phags-pa, Mongolian, and Ogham; I will ignore them for the 
time being, unless someone volunteers to try them out with PDF::Builder 
software (next release, 3.019, or GitHub after today). I'll just hope 
that HarfBuzz handles vowel (spacing) marks correctly (on the same 
"line" as the consonant?), and if anyone reports that it's incorrect, 
I'll see what I can do. I'm also assuming that Arabic and related 
languages will have more or less the same rules as Hebrew (again, if 
documented as incorrect, I'll see what I can do). Column direction 
remains to be seen, and might be dependent on the specific language. 
PDF::Builder does not yet support multi-column vertical text, but I'll 
probably default to right-to-left and give an option for left-to-right. 
BTT is supported, if any language needs to use that.

Again, thanks! Phil