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

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Cc: emacs-devel@gnu.org
> Date: Fri, 26 Aug 2011 22:53:36 -0400
> 
> > There's a similar issue with file names: /abcd/ABCD/XYZ will be
> > displayed as /abcd/ZYX/DCBA.
> 
> IIUC in an English paragraph this should be displayed as /abcd/DCBA/ZYX
> but in a Hebrew paragraph it should be displayed as ZYX/DCBA/abcd/, right?

I think it should be displayed as /abcd/DCBA/ZYX in both cases.  When
a file name is mentioned in a R2L paragraph, it will need to be
embedded in LRE..PDF, as I did with the URL near the end of TUTORIAL.he.

> So embeddings should not be used too much, and/or should only be used
> dynamically (jit-lock-style) and implicitly (e.g. not copied by
> kill-region).

It depends.  If only part of the embedded text is copied, then the
directional formats should be dropped, indeed.  But if all of it is
copied, they should be kept, to preserve the visual appearance.

So I guess we will need to set filter-buffer-substring-functions to
something non-nil by default?  Or maybe modify filter-buffer-substring
itself to remove these characters as needed?