Plain text custom fraction input

[Khaled Hosny]

On Wed, Jul 22, 2015 at 09:00:38AM +0200, Marcel Schneider wrote:
> On 21 Jul 2015, at 18;42, Doug Ewell  wrote:
> 
> > As explained in TUS 7.0, §6.2 ("General Punctuation"), p. 273, U+2044
> > FRACTION SLASH is intended for use with Basic Latin digits, or other
> > digits with General Category = Nd. The superscript and subscript
> > presentation forms have General Category = No.
> 
> That is was bugs me, that this kerning fraction slash is presented to
> us as to be used with plain digits, that overlap the fraction slash in
> proportional fonts. That recommendation is inconsistent with plain
> text encoding. Following TUS, anybody who uses U+2044 must use a
> fraction formatting feature. I know this from the time I'd got the
> valid demo version of some Desktop Publishing software. The feature
> wasn't flagged by the fraction slash, and on the other hand, the
> feature worked with the common slash U+002F too. It's a formatting
> command like superscript or underline.

Some layout engines, like HarfBuzz, automatically turn on the required
OpenType features for proper fraction rendering when fraction flag is
used. If the font has “numr” and “dnom” features, HarfBuzz will turn
them on for the <digits><fraction slash><digits> sequence. IMHO, that is
the most Unicode-compliant approach and other engines should do the
same.

Regards,
Khaled