> Providing > private use characters with a default ccc other than 0 would > open combining classes for private use in a manner that > could be consistently normalized regardless of whether > the implementation was a party to the private use or not.
Note that these could *not* be any existing PUA code points, for the folowing reason. Currently: code point: 0061 100001 0323 ccc 0 0 220 Normalized to NFD: <0061, 10001, 0323> Say we decided that some block of PUA characters, including U+100001, would have ccc=230, as a kind of private-use combining mark above, at least as a "default" property. Future: code point: 0061 100001 0323 ccc 0 230 220 Normalized to NFD: <0061, 0323, 10001> Clearly this is disallowed by normalization stability guarantees. So if you or anybody else is proposing such a change, make sure that it is in the context of defining a *new* block of private use characters, off the BMP and not Planes 15 or 16. Convincing anyone on the committees to accept yet another block of PUA code points, particularly with default properties that SC2/WG2 doesn't even recognize, is going to be a very tough sell. But don't make your proposal an even tougher sell by making it an outright violation of normalization stability as well. --Ken
