OverStrike control character

[James Kass]

On 2020-06-19 4:37 AM, abrahamgross--- via Unicode wrote:
> Then how does the ZWJ (zero width joiner) work?

It’s considered punctuation even though it has control and format 
aspects.  ZWJ is default ignorable.  ZWJ requests a more joined form of 
a character string for the display if a more joined form is available in 
the font/rendering system.  If a more joined form is not available the 
display will be the same as if the ZWJ was not part of the character 
stream, and no harm done.  The point being that the author requested a 
more joined form and this authorial intent is preserved in the text/data.

The ZWJ might be a good way to achieve over-striking.  For example, the 
string “Respec‍tfully” has a ZWJ inserted between the “c” and the “t”.  
If you had a font which substituted a “c-t” over-strike for that string, 
your display could show it.  If you had a font which substituted a “c-t” 
ligature for that string, that ligature would be displayed.  Otherwise 
the string “Respec‍tfully” would look the same as the string “Respectfully”.

(Heh, the Thunderbird spell-checker chokes on the two instances with ZWJ.)