bug#27544: [External] : bug#27544: 25.1; Visualization of Unicode bidirectional marks

[Drew Adams]

> > > Emacs supports 12 Unicode bidirectional marks (ALM, RLM, LRM, LRE,
> > > RLE, LRO, RLO, PDF, FSI, LRI, RLI, and PDI), each of which displays as
> > > a very thin space. This raises two problems.
> >
> > Perhaps there should be a minor mode to display these characters more
> > clearly, because they can be pretty confusing to deal with.
> >
> > What would be the best way to implement such a mode?  Change
> > `glyphless-char-display' buffer-locally?
> 
> Yes, I think so.

(Not following this bug thread.  Ignore if not helpful.)

Would something like what's in `modeline-char.el' help?

There's a minor mode that shows, in the mode line, the
char  after point, together with its hex Unicode code
point.  E.g., for char `e' it shows e=000065.

* If you click `mouse-1' on the lighter then full
  information about the char is shown in `*Help*',
  including the font and faces used for the char.

* If you click `mouse-2' on the lighter then the
  char is copied to the secondary selection.

* If you click `mouse-3' on the lighter then the
  char is shown enlarged in a tooltip.

https://www.emacswiki.org/emacs/download/modeline-char.el

For this bug, maybe some indication like `FSI' would
help - instead of or in addition to the code point.