Re: Display question

[Michael Welsh Duggan <md5i@md5i.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Michael Welsh Duggan <md5i@md5i.com>
>> Date: Wed, 08 Jun 2011 01:55:54 -0400
>> 
>> Afterward, I get a character that looks like a double-boxed RLO.  Image
>> included:
>> 
>> Is this expected?  If I just do (insert RLO RLO RLO) a few times in a
>> non-font-locked buffer, I get a box around RLO, with a tiny space
>> between the boxes, and not the double box seen here.
>
> The difference between these two use cases is that characters
> delivered from display tables are not subject to the treatment we give
> to "glyphless characters", which is what u+200b ZERO WIDTH SPACE is.
> You expect this character to be displayed as a thin space (probably to
> get the boxed "RLO" look prettier), but this thin space will only show
> when u+200b is treated as a glyphless character, which can happen when
> it comes from the buffer, but not from a display table.

[...]

> Btw, you cannot expect that u+200b is displayed as a thin space,
> because the user could change that via glyphless-char-display-control,
> which see.  So this particular use of u+200b is questionable to begin
> with, IMO.

I wasn't actually thinking it would appear as a space when I initially
tried it.  I was using it to separate two runs of character properties
so the boxes wouldn't join if they were next to each other.  (This does
and does not work if I set u+200b to zero-width.  I think this confuses
the display mechanism a little.)  I did not know about
glyphless-char-display, which seems to have the feature I was trying to
implement built in.  Thanks for the help.

(I was playing around with ideas on how to display and undisplay bidi control
characters, as you might have guessed.)

-- 
Michael Welsh Duggan
(md5i@md5i.com)