Re: bidi-display-reordering is now non-nil by default

[Chong Yidong]

Eli Zaretskii <address@hidden> writes:

>> I'll have to think more about it, but I am not sure it's a good idea.
>> The display property is already used for a lot of other unrelated
>> purposes, like variable-width spaces.  So if you want to mark out a bidi
>> segment on a stretch of text that already has other display properties
>> present, you'd currently have to do some nasty merging of display specs.
>
> I don't see any need for any merging.  We already process display
> specs on before- and after-strings, and the same code can be used
> here.  IOW, those other display specs will be simply processed as part
> of displaying the stretch of text covered by the bidi display spec.

Suppose you have a stretch of text which includes characters with no
text properties plus a space with the display property

   '(space :width 3.0)

Suppose you want to use a display text property to mark that stretch of
text as a single bidi segment.  You'd add '(bidi-foo blahblah) to most
of the characters, but the property on the space character would have to
be something like

   '((bidi-foo blahblah) (space :width 3.0))

to avoid clobbering the pre-existing space display spec.

Obviously it is possible to do this, but it is just way cleaner and more
user-friendly to use a separate property for this purpose.