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

[Eli Zaretskii]

> From: Stefan Monnier <address@hidden>
> Cc: Chong Yidong <address@hidden>,  address@hidden,  address@hidden
> Date: Tue, 16 Aug 2011 10:03:15 -0400
> 
> > "Higher level protocols" don't include futzing with bidirectional
> > properties of characters.  "Higher level protocol" means some means to
> > determine segment boundaries other than segment separator characters
> > that are part of the text.  Translated into Emacs-speak, this means we
> > need a variable that, when bound to some special value, instructs the
> > reordering engine to treat certain characters as segment separators.
> 
> Maybe we then need a way to declare some chars (such as SPC,
> punctuation, string markers, comment markers, ...) as
> segment boundaries.

As I wrote, implementing this for an arbitrary set of characters is
easy.  But the problem is that any character which we declare a
segment separator will behave like that everywhere in that buffer.  If
the same characters appear in a different context, where we do want
the reordering, we are screwed.

For example, suppose we declare SPC a segment separator.  Then this:

  (foo ARGA ARGB)

will be displayed correctly, but blanks in doc strings in the same
buffer will mess up the display, because something like this:

  "FOO BAR BAZ"

will be displayed like this:

  "OOF RAB ZAB"

whereas we want this:

  "ZAB RAB OOF"