Re: [emacs-bidi] Re: Callbacks?

[Eli Zaretskii]

> Date: Thu, 01 Dec 2005 20:35:42 +0900
> From: Martin Duerst <address@hidden>
> Cc: address@hidden
> 
> There is definitely a need for some
> code that does the actual reordering, even if the directionality
> can be defined as some text property. Same for colors; there
> needs to be some C code that actually takes the color property
> and produces the color on the screen.

If you are thinking about using text properties to store the
character's directional properties, the ones specified in the Unicode
database, then that sounds like a waste of resources: the Unicode
version of Emacs already reads that database, so why repeating the
data in another data structure?

>  >> Now the interesting possibility presents itself, which is to add
>  >> Unicode-related "special" (ie. built-in) text properties.  In
>  >> particular, directional class.
>  >
>  >Not a good idea: text properties are considered part of the text, so
>  >they are, e.g., copied together with the characters when you
>  >copy/paste text.
> 
> If this is used with a mode, this should not be a problem:
> The mode reanalyzes the pasted text and fixes things up.

That's not how text properties are handled now in Emacs.  It would
slow down Emacs, for one thing.  In any case, this is using text
properties for something they were not designed to do.  (There are
additional complications, e.g. text properties cannot nest.)

>  >Use of text properties as part of the reordering (specifically, to
>  >store the Unicode bidi embedding levels) was discussed here in the
>  >past, and the conclusion was that we should not use them.  Again,
>  >please read past discussions.
> 
> I'll gladly do that. Can you point to the relevant section
> of the mailing list archives?

Sorry, I found out these discussions were held before emacs-bidi was
handled by mailman, so the public archives don't include the relevant
messages.

If you have access to gnu.org machines, I can tell you where to fetch
the old archives.  Alternatively, I could upload them to some place
you can access, if you tell me where.  The old archives are 5 files,
each one 50-80KB.