Mongolian Joining Type

[Richard Wordingham]

On Wed, 5 Aug 2015 17:26:57 -0700
Roozbeh Pournader <roozbeh at google.com> wrote:

> On Wed, Aug 5, 2015 at 3:49 PM, Richard Wordingham <
> richard.wordingham at ntlworld.com> wrote:

> > 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.

> That seems contradictory with what the Core Specification says ...

Please tell me where.  I couldn't find anything helpful when I looked.

> ... and
> how I understand the MVS. Would you please provide examples for it
> behaving like a T or D?

In isolation, the form of the vowel after MVS is produced by the
following combinations:

1820 180B; second form; final # MONGOLIAN LETTER A

1821 180B; second form; final # MONGOLIAN LETTER E

(They're the same glyph.)

For these to be a final, as opposed to an isolated form, MVS must be T,
D or L.

In isolation, the form of the consonant before MVS is produced by the
following combinations:

1828 180C; third form; medial # MONGOLIAN LETTER NA

182C 180D; fourth form; medial # MONGOLIAN LETTER QA

182D 180C; third form; medial # MONGOLIAN LETTER GA

1836 180C; third form; medial # MONGOLIAN LETTER YA

For these to be medial, MVS must be T, D or R. 

Consequently, MVS must be T or D!

If there are no variation selectors, it doesn't really matter what MVS
is, provided the contextual changes triggering on MVS change all four
forms (isolated, initial, medial and final).

The Mongolian Baiti font is in the process of abandoning support for the
above variations in accordance with a deeply buried proposal to tinker
with the encoding of Mongolian.  (Unicode string encodings aren't stable
until there's a large volume of use or a change would be too
embarrassing.)

Richard.