Re: RTL PUA?

On 08/19/2011 07:13 PM, Michael Everson wrote:
> This is a very good question.

It seems Michael speaks tongue-in-cheek.

I personally don't see the point in allocation RTL areas in the PUA. It
is after all the *P*UA. Do you expect rendering engines to support the PUA?

Yeah OK maybe simply base+diacritic stuff or even ligatures would be
easy to do via simple substitution rules in tables, but how about glyph
reordering?

Indic scripts involving reordering and split-positioning vowel signs
can't be handled by placing them in the PUA. (I mean one doesn't expect
*published* rendering engines to reorder such PUA-Indic codepoints while
one can always write custom code to do so for one's own purpose).

In what way are RTL scripts different that proper rendering should be
supported for them even though they are in the PUA?

If you want proper rendering in terms of bidi formatting and glyph
reordering etc you should make a proposal for official encoding. The PUA
will not help.

Ergo there is no scope for specifying directionality for PUA code-points.

At least that is MHO.

However I do wonder what the following lines are doing in
UnicodeData.txt specifying BC=L for them:

E000;<Private Use, First>;Co;0;L;;;;;N;;;;;
F8FF;<Private Use, Last>;Co;0;L;;;;;N;;;;;
F0000;<Plane 15 Private Use, First>;Co;0;L;;;;;N;;;;;
FFFFD;<Plane 15 Private Use, Last>;Co;0;L;;;;;N;;;;;
100000;<Plane 16 Private Use, First>;Co;0;L;;;;;N;;;;;
10FFFD;<Plane 16 Private Use, Last>;Co;0;L;;;;;N;;;;;

I also wonder what the following below
http://unicode.org/reports/tr9/#Bidirectional_Character_Types means:

Private-use characters can be assigned different values by a conformant
implementation.

-- 
Shriramana Sharma