OverStrike control character

[Mark E. Shoulson]

On 6/20/20 9:31 PM, abrahamgross--- via Unicode wrote:
> Basically, yes. unicode has plenty of basic geometric shapes throughout that can be utilized to build interchangeable (and non-PUA) characters. (if Classical Yi ever get accepted, then youll be able to use just about any shape out there for your overstriking needs (the proposal lists over 88k new chars!))

Essentially "painting" with characters.  Which wouldn't work in a 
consistent fashion (you point out yourself it won't render things the 
same if you use different fonts) and would be MUCH more complicated to 
use than just encoding some vector drawing language with Unicode 
code-points (which has been suggested, and has its own raft of issues).  
Which set of Yi characters will paint just the picture of George 
Washington that I want...?  Easier to paint it!

You had previously said

>> What about overstriking a LTR character with a RTL one, or vice-versa?  Which way does the text go after that?
>>
> The text after that goes in the direction of the text afterwards. So for “L←י‎א‎ב” its gonna look like “[L‌י‎]‎ב‎א‎” and for “L←יab” its gonna look like “[Lי]ab”. Meaning that only the very next letter gets overstruck, and anything afterwards continues on like it would normally.
It's not about what happens if you put a strong LTR or RTL character 
afterwards.  Those always carry their own directionality!  Read up on 
the Unicode Bidi algorithm.  The direction of a stream of text is 
stateful, and some characters adapt themselves to what the current 
directionality is.  If I have A←א, what state does that leave things 
in?  Is it the same or different from א←A?

~mark

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