Zero-Width Joiner U+200D

[Asmus Freytag]

On 2/21/2023 1:19 AM, Jukka K. Korpela via Unicode wrote:
> My interpretation of this is that ZWJ should have no effect when it 
> does not appear between two graphic characters.

Not what I remember as the intent when we introduced the character way 
back when. Clearly one of the design features was to also support 
"didactic" formatting, that is, bracketing a character with joiners or 
non-joiners to be able to show positional forms in isolation.

While later compromises forced the acceptance of the compatibility 
forms, it was never anticipated that there would be a use case for them 
that couldn't be realized with standard characters.

I see where you might come to your interpretation of the text as 
written, but the cases where you might reasonably need adjacent 
characters to be able to get the requested effect would be more for 
things like ligatures where it doesn't make sense to display a single 
character "as it would appear in a ligature" because, unlike positional 
forms, that concept is not well defined.

(I don't know to what degree in actual layout the positional forms 
themselves are dependent on knowing the adjacent character, and whether 
that makes it less straightforward to display a "nominal" positional 
form, as in a generic "medial ain").

A./
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