Combining Marks and Variation Selectors

Mark Davis ☕️ via Unicode unicode at
Sun Feb 2 13:43:18 CST 2020

I don't think there is a technical reason for disallowing variation
selectors after any starters (ccc=000); the normalization algorithm doesn't
care about the general category of characters.


On Sun, Feb 2, 2020 at 10:09 AM Richard Wordingham via Unicode <
unicode at> wrote:

> On Sun, 2 Feb 2020 07:51:56 -0800
> Ken Whistler via Unicode <unicode at> wrote:
> > What it comes down to is avoidance of conundrums involving canonical
> > reordering for normalization. The effect of variation selectors is
> > defined in terms of an immediate adjacency. If you allowed variation
> > selectors to be defined for combining marks of ccc!=0, then
> > normalization of sequences could, in principle, move the two apart.
> > That would make implementation of the intended rendering much more
> > difficult.
> I can understand that for non-starters.  However, a lot of non-spacing
> combining marks are starters (i.e. ccc=0), so they would not be a
> problem.  <starter, variation selector> is an unbreakable block in
> canonical equivalence-preserving changes.  Is this restriction therefore
> just a holdover from when canonical equivalence could be corrected?
> Richard.
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