Combining Marks and Variation Selectors

[Richard Wordingham via Unicode]

On Sat, 1 Feb 2020 17:59:57 -0800
Roozbeh Pournader via Unicode <unicode at unicode.org> wrote:

> They are actually allowed on combining marks of ccc=0. We even define
> one such variation sequence for Myanmar, IIRC.
> 
> On Sat, Feb 1, 2020, 2:12 PM Richard Wordingham via Unicode <
> unicode at unicode.org> wrote:  
> 
> > Why are variation selectors not allowed for combining marks?  I can
> > see a reason for them not being allowed on characters with non-zero
> > canonical combining classes, but not for them being prohibited for
> > combining marks that are starters, i.e. have ccc=0.

Ah, I missed that change from Version 5.0, where the restriction was,
'The base character in a variation sequence is never a combining
character or a decomposable character'.  I now need to rephrase the
question.  Why are marks other than spacing marks prohibited?

Richard.