Re: [Emacs-diffs] /srv/bzr/emacs/trunk r105429: New function `string-mark-left-to-right' for handling LRMs.

[Eli Zaretskii <eliz@gnu.org>]

> From: Kenichi Handa <handa@m17n.org>
> Cc: cyd@stupidchicken.com, monnier@iro.umontreal.ca, emacs-devel@gnu.org
> Date: Wed, 17 Aug 2011 08:57:49 +0900
> 
> > Would it be a good idea to add such categories to the standard
> > category table?  IOW, why do we need a special category table to
> > search for these characters?
> 
> We can define at most 95 categories in one table, and, in
> the standard category table, we already defined 41
> categories.
> 
> For bidi, we need at least 18 categories (there are 18 bidi
> classes) and a few more for combinations.  Adding all of
> them to the standard category table makes the remaining
> category space less than half of the whole space.  So, I
> think we should be careful.

I didn't mean to add each bidi type as a separate category (there are
19 of them, btw).  I did mean to carefully define the most frequently
needed categories, like the one which started this discussion, and add
only those.  The gain would be that we won't need to use
with-category-table around code which needs to search for characters
by their bidi types, and we will be able to combine bidi-related
categories with other standard categories in the same regular
expression.

One possible set of categories is just the 3 bidi categories defined
by UAX#9: Strong, Weak, and Neutral.  We'd probably need to split the
first one in two, depending on directionality, so Strong_R, Strong_L,
Weak, and Neutral would be my initial guess.

However, we should gather more experience before we decide.

> In addtion, adding them to the standard category table means
> we can't select a proper category mnemonic character.

?? We can use any one that is currently unused, no?  Those that are
used are shown by describe-categories, right?  Or am I missing
something?