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

[Yair F]

On Wed, Aug 18, 2010 at 5:06 AM, Kenichi Handa <address@hidden> wrote:
> I think it's about the time to decide how to display these
> formatting characters: LRE, RLE, LRO, RLO, PDF, LRM, RLM.
>

This is not a bidi-specific issue.  It is possible that these characters
and other Unicode control characters needs to be trated as non-visiblle
characters. The assitional characters are CGJ, IAA, IAS, ZWNBSP (BOM),
IAT LSEP, PSEP, WJ, Invisible Operators, ans all Zero width characters:
ZWSP, ZWNJ, ZWJ.

All of these characters modify the environment aboud them but do not
display glyphs. In some way they are like the TAB character.

I am thinking of extending whitespace.el to make them visible if the
user wishes, but IMO, they should bot be visible by default. See the
impact on the HELLO fle.

> (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.
Yes, but currently the cursore is "gone" if it is on invisible character.

>
> (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?).
>

These modes seems less usable.

> (4) fancy-visible-mode
>
> Show them by a glyph something like what you can see by this code:
>
Yes, SI 1452 indeed specify characters look U21B2 and U21B3 for
keyboard marking for LRM and RLM.