Proposing new arrow characters with Bidi_Mirrored=Yes

[Nitai Sasson]

I just stumbled upon this:

https://www.unicode.org/versions/Unicode16.0.0/core-spec/chapter-23/#G13001

> Three pairs of deprecated format characters are encoded in this block:
>
> Symmetric swapping format characters used to control the glyphs that depict characters such as “(” (The default state is activated.)
>
> [...]
>
> Symmetric Swapping. The symmetric swapping format characters are used in conjunction with the class of left- and right-handed pairs of characters (symmetric characters), such as parentheses. The characters thus affected are listed in Section 4.7, Bidi Mirrored. They indicate whether the interpretation of the term LEFT or RIGHT in the character names should be interpreted as meaning opening or closing, respectively. They do not nest. The default state of symmetric swapping may be set by a higher-level protocol or standard, such as ISO 6429. In the absence of such a protocol, the default state is activated.
>
> From the point of encountering U+206A INHIBIT SYMMETRIC SWAPPING format character up to a subsequent U+206B ACTIVATE SYMMETRIC SWAPPING (if any), the symmetric characters will be interpreted and rendered as left and right.
>
> From the point of encountering U+206B ACTIVATE SYMMETRIC SWAPPING format character up to a subsequent U+206A INHIBIT SYMMETRIC SWAPPING (if any), the symmetric characters will be interpreted and rendered as opening and closing. This state (activated) is the default state in the absence of any symmetric swapping code or a higher-level protocol.

These deprecated format characters differ the ones proposed now in the following ways:
- They only apply to characters that have the Bidi_Mirrored property, meaning they don't solve the use cases raised.
- They apply to an entire span of text, whereas the proposed characters bind to a single preceding character each time.
- It is ambiguous, at least to me, whether symmetric swapping should be inhibited or activated after U+206B ACTIVATE SYMMETRIC SWAPPING .. U+206A INHIBIT SYMMETRIC SWAPPING. The proposed characters would leave no ambiguity.

As I mentioned, I will share a more complete description of the proposal in an email under a new title soon. If anyone would like to help draft it, contact me privately.

Thanks,
Nitai
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