On Oct 13, 2004, at 1:42 PM, Eric Muller wrote:
Going back to the original scenario, to make my point clearer:
System A, a subset of FileMaker, has {U+0065, U+0303, U+1EBD} as its repertoire. When presented with the input <U+0065, U+0303>, it produces the output <U+1EBD>.
System B, my rendering system, has {U+0065, U+0303} as its repertoire. When presented with the input <U+0065, U+0303>, it produces a correct rendering. When presented with the input <U+1EBD> it outputs a smiley.
Both systems are conformant (I would hope), yet putting them together does not mean that the result is automatically conformant, even on the intersection of their repertoire. Hence, one cannot attribute the problem that Richard is seeing to either system. The problem belongs to Richard, when he did put the two systems together.
Well, if it belongs to me, I'll happily give it away for free to anyone willing to take it off my hands.
If we want some automatic guarantee of conformance for combinations of conformant systems, then we need at least to impose that the repertoire supported by conformant implementations be closed under canonical equivalence. Such a condition is not there today. It has interesting consequences: e.g. U+2FA1C is canonically equivalent to U+9F3B, so the BMP is not closed under canonical equivalence, so no conformant system could make its repertoire exactly the BMP.
If someone wants to normalize my text into precomposed things, that's all well and good, so long as there's a fallback mechanism for rendering via a font which may have only the decomposed parts.
I don't know if this is the same as saying that "we need at least to impose that the repertoire supported by conformant implementations be closed under canonical equivalence".
But, I say this after spending *way* too much time yesterday adding precomposed things to my font. You might think that I can rationalize it, thinking that now the diacritic placement will be somewhat better than it was before. But I thought the diacritic placement was adequate to begin with. And I can't predict what new precomposed things I might need to support in the future.
-Richard
