[tech] Zero-width characters and tracking via pasted text

[nervuri]

It might be interesting to also test our e-mail clients, so below you'll
find all zero-width Unicode characters I've gathered so far, placed
between underscores.

First, as a point of reference, here are a few positive-width Unicode
characters:
0020: _ _ | 00E9: _é_ | 03A9: _Ω_ | 5B57: _字_ | 1F407: _🐇_

# Zero-width characters

 061C: _؜_

 180E: _᠎_

 200B: _​_
 200C: _‌_
 200D: _‍_
 200E: _‎_
 200F: _‏_

 202A: _‪_
 202B: _‫_
 202C: _‬_
 202D: _‭_
 202E: _‮_

 2060: _⁠_
 2061: _⁡_
 2062: _⁢_
 2063: _⁣_
 2064: _⁤_
 2066: _⁦_
 2067: _⁧_
 2068: _⁨_
 2069: _⁩_

 206A: __
 206B: __
 206C: __
 206D: __
 206E: __
 206F: __

 FEFF: __
 FFF9: __
 FFFA: __
 FFFB: __

E0001: _󠀁_

E0020: _󠀠_
... (E0020–E007F used for invisibly tagging texts by language)
E007F: _󠁿_

This is probably not a complete list.  Contact me if you know of any
others.

Unicode currently contains 143,859 characters.

Unicode Character Database:
https://www.unicode.org/Public/UCD/latest/