On Sun, 2 Feb 2020 07:51:56 -0800 Ken Whistler via Unicode <unicode@unicode.org> 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.