Proposing new arrow characters with Bidi_Mirrored=Yes

[Eli Zaretskii]

> Date: Tue, 08 Apr 2025 17:56:09 +0000
> Cc: "'Asmus Freytag'" <asmusf at ix.netcom.com>, unicode at corp.unicode.org
> From: NeatNit via Unicode <unicode at corp.unicode.org>
> 
> > If replacing "->" by an arrow character can change its direction, isn't it up to the autocorrect software to analyze the bidi context and select the correct arrow? The rule should be to select whatever substitution gives the same appearance (direction) as what the user would see for the string they typed.
> 
> The problem is this replacement is done (as far as I know) outside of any rendering context, when the text is just a sequence of character codes. It's not reasonable to know which direction the text goes. Sometimes it's completely impossible, if the text direction depends on context that isn't available at the time of replacement.

The above is strictly speaking inaccurate.  Any serious text rendering
nowadays requires a shaping engine, such as HarfBuzz, and ligation of
"->" into "→" would be done by such a shaper in cooperation with a
font that supports ligatures.  The shaping engine _is_ aware of the
bidi context and the script of the text it shapes, so it could in
principle mirror the arrow.

The question is whether the cases where mirroring is the correct
rendering by far outweigh the non-mirroring cases.  If yes, the shaper
could mirror and expect text which wants to avoid that use directional
override controls.  If not, mirroring will not make sense.