[emacs-bidi] Treatment of LRE,RLE,LRO,RLO,PDF,LRM,RLM

[Kenichi Handa]

I think it's about the time to decide how to display these
formatting characters: LRE, RLE, LRO, RLO, PDF, LRM, RLM.

Eli wrote:
> Anyway, characters such as LRM should be automatically
> composed with the character that follows them, and then
> they will be invisible.

But, if we do that, users lose control exactly which part of
text he selects or delete, exactly where to insert a text
because he can't put cursor between LRM, etc. and the
following character.

I can think of these modes:

(1) invisible-mode (perhaps the default)

Hide them, for instance, by
  (aset standard-display-table #x202e [])

Then, you have to type C-f or C-b twice to pass over those
characters.  That means users can still put cursor anywhere
if he moves cursor carefully.

(2) light-visible-mode

Show them by a space of 1-pixel width.

(3) heavy-visible-mode

Show them, for instance, by
  (aset standard-display-table #x202e [?[ ?R ?L ?O ?]])
perhaps with some color attribute (forground? underline?).

(4) fancy-visible-mode

Show them by a glyph something like what you can see by this code:

(make-face 'small)
(set-face-attribute 'small nil :height .5)
(set-face-attribute 'small nil :box t)
(insert (propertize (compose-string "RLO" 0 3 '(?O (tc . br) ?R (tr . tc) ?L))
                    'face 'small ))

---
Kenichi Handa
address@hidden