23AF HORIZONTAL LINE EXTENSION: glyph or variation selector?

[Whistler, Ken]

Yucca noted:

> > These glyphic pieces of symbols are only relevant and useful
> > in the context of mathematical typesetting programs like TeX.
> 
> I’m not sure whether TeX uses such characters at all. TeX is oriented
> towards typesetting glyphs, often not caring that much about abstract
> characters. 

Yes, I'm not claiming there is any actual use of U+23AF in TeX per se.

The original source of U+23AF, by the way, was as a compatibility
mapping character for the PostScript "arrowhorizex". See octal 276
in the symbol font encoding for PostScript. The original proposal
for the set of these can be seen in L2/99-346 in the UTC
document register. The whole set of these pieces was included
into the repertoire of mathematical symbols under discussion
at the time, and was eventually published as part of Unicode 3.2.

--Ken