Proposing new arrow characters with Bidi_Mirrored=Yes

[Eli Zaretskii]

> Date: Thu, 10 Apr 2025 19:58:42 -0400
> From: "Mark E. Shoulson via Unicode" <unicode at corp.unicode.org>
> 
> The "proposed solution", as I see it, is there is some character that attaches to the previous character (or
> probably the previous base character or grapheme cluster, if it comes to that), and flags it as subject to BiDi
> mirroring.  I imagine this wouldn't necessarily be available for EVERY SINGLE CHARACTER in Unicode; we
> don't need to make sure it's possible to write a mirror-reversed ネ or @ or whatever (I mean, unless we do
> need those), but presumably some selected list of characters, mainly arrows and things like directional math
> operators and possibly some directional emoji.  This might be a good idea?  I don't know all the possible
> ramifications.  And I'm not even sure that considering it like a variation selector would be wrong.  If it isn't
> honored, what's the damage?  Possibly huge, since assigning אחת←שתיים is drastically different from
> אחת→שתיים (and אחת, not אחד, to at least be consistent, right?) but maybe that's acceptable anyway, if the
> author understands that going in.

Once again, AFAIU the proposed solution is incomplete: it provides an
indication that a character should be mirrored, but not with what
character to mirror it.  For characters for which Unicode doesn't
specify Bidi_Mirroring_Glyph, how would the rendering application know
what glyph(s) to show when mirroring is required?