Mongolian Joining Type

[Richard Wordingham]

On Wed, 5 Aug 2015 12:48:59 -0700
Roozbeh Pournader <roozbeh at unicode.org> wrote:

> These were the original proposals:
> http://www.unicode.org/L2/L2012/12202-shaping.txt
> http://www.unicode.org/L2/L2012/12360-mong-shaping.txt
> (with considerable UTC discussions).
> 
> A good trick is going through the posted UTC minutes and searching
> for the topic you are interested in. Or just do Google searches,
> restricting your search to site:unicode.org and adding "L2" to the
> search string.

So how did you obtain the joining types for U+180E MONGOLIAN VOWEL
SEPARATOR (MVS) (specified as U) and U+202F NARROW NO-BREAK SPACE
(NNBSP) (defaulting to U)?  Did you study the Mongolian variation
sequences?  Did someone tell you how they behaved?

One problem from your source is that UTC discussions are rarely
minuted.  The decisions are recorded, but not the reasoning.  The
other, is that I am interested in what the state of affairs was before
the change.  I have a suspicion that no-one had defined the meaning of
the joining forms because 'it was obvious'.

There are arguments going round that NNBSP acts as though joining to the
following character (the one to the right in horizontal text), which
would make it joining type L.  MVS seems a bit of an oddity.  The
standardized variants make most sense if it is of joining type T
('transparent') or D ('dual_joining'), but a further contextual
substitution is still required if there is no variation selector.

Richard.