Superscript and Subscript Characters in General Use

[Doug Ewell]

Marcel Schneider wrote:

> This is because even complemented with UAXes and TRs, the Core
> Specifications cannot cover the whole practice. It seems that to stay
> inside reasonable limits, a significant number of usage cases have
> been left out, e.g. the mentioned use of plain text for styled custom
> vulgar fractions is a recognized practice, but stays persistently
> excluded from TUS.

I don't understand the relevance to vulgar fractions.

Much of this thread has dealt with Basic Latin characters that have no
superscript or subscript clones, and how their absence prevents certain
passages from being representable in plain text. This is your basic
debate over what constitutes plain text.

As explained in the July 2015 thread about vulgar fractions, TUS
sections 6.2 and 22.3 thoroughly explain the use of U+2044 FRACTION
SLASH with normal "Nd" digits. If I want to write "ninety-nine and
forty-four one-hundredths," with the non-precomposed vulgar fraction, I
can write "99 44⁄100" and be fully compliant with the Standard. This
has nothing to do with what is and isn't plain text.

The fact that many current rendering systems can't render this correctly
is an implementation matter, though a hard-to-fix one. (Note that the
fallback display is perfectly readable and correct, unless you see a box
for U+2009.)

The fact that TUS doesn't sanction the use of U+2044 with superscript
and subscript digits, which I imagine Marcel was alluding to, is
irrelevant. TUS is a character encoding standard, not a glyph encoding
standard.

If Marcel is talking about distinguishing between horizontal and
diagonal slashes in vulgar fractions, this is still not a question of
plain text. However, in the emoji era, this type of presentation
variation has become something that Unicode cares about, and so it might
be handled in some way in the future, such as with a variation selector.
I suspect this mechanism has been "excluded from TUS" because it doesn't
yet exist.


--
Doug Ewell | Thornton, CO, US | ewellic.org