How was the table of width in [format] derived? 

We have 2 issues here: Lack of explanation in the standard makes it hard to evolve that table,

and it does require maintenance as the Unicode standard evolves.

Reading the intent of https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p1868r2.html,

We do want: 

https://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c 

I think a better specification would be given that we have a floating reference to UAX44,

to say that codepoints that have the Unicode property "Emoji_Presentation" or 

East_Asian_Width="W"  have a width of 2.

This ensures implementation remains coherent as Unicode evolves.

Thanks, 

Corentin