Plain text custom fraction input

[Richard Wordingham]

On Wed, 22 Jul 2015 09:00:38 +0200 (CEST)
Marcel Schneider <charupdate at orange.fr> 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.

Implementing FRACTION SLASH is fiddly, and formally it is impossible in
OpenType - the lookup tables can only cope with a finite range
of numerator and denominator lengths.  The next problem is what feature
to put it under.  Microsoft Word is notorious for preventing users from
using ligatures in Latin script text, though that restriction has been
relaxed.

One of the touted capabilities of Microsoft's Universal
Script Engine is the rendering of cartouches for Egyptian hieroglyphs.
However, the interface specification makes no mention of special
handling for them - I can only assume that the capability arises
through the enabling of certain features.  Egyptian hieroglyphs are
currently a simple script - it lacks essential support for writing the
script seen on Egyptian monuments.  (I'm not entirely sure of the
correct bidi classification of the original hieroglyphs - they should
probably be weakly right-to-left, not strongly left-to-right.  Strong
left-to-right may, however, be appropriate for most printed hieroglyphs
- I've even seen plain text hieroglyphs running left to right on a page
whose primary script is Arabic.)

Richard.