L2/01-268

Asmus Freytag <asmusf@ix.netcom.com> 
Sent: Wednesday, June 27, 2001 7:34 PM

UTC#88 Agenda item for US comments: Variation selector


The specification for the variation selectors needs to be formalized in
some ways. The following is a rather terse write-up of the issues,
hopefully sufficient to serve as a paper for the UTC to formally adopt
these recommendations. (They derive from discussion on unicore and
editorial committee):

Variation selectors need to be combining characters in order to work
properly. UTC/L2 needs to request a corresponding change from WG2 as part
of the comments.

In terms of Unicode properties, the combining class for VS1 and the
Mongolian Free Variation selectors should be set to 0.

Finally, the action of variation selectors that do not immediately follow a
base character for which their use has been explicitly specified, is
undefined.

It should be the policy of UTC and WG2 to not define VS1 or FSVn in
combination with combining characters.

In terms of Unicode, no variation selector affects joining behavior.
(Transparent class).

Unsupported VS: (i.e. lack of support in implementation): recommended
behavior is to treat as if it has a ZW glyph.

Ill-placed VS: The same, ignore as much as possible in other processes, but
some processes, e.g. normalization, will be affected.