I agree with that analysis.
Mark <https://plus.google.com/114199149796022210033> * * *— Il meglio è l’inimico del bene —* ** On Mon, Nov 26, 2012 at 1:53 PM, Whistler, Ken <[email protected]> wrote: > Actually, I think the omission here is the word "canonical". In other > words, Section 16.4 should probably read: > > "The base character in a variation sequence is never a combining character > or a *canonical* decomposable character." > > Note that with this addition, StandardizedVariants.txt poses no > contradiction, because all of the decomposable character instances noted > are compatibility decomposable characters. > > The main concern here with this restriction is to ensure that one doesn't > end up with conundrums involving canonical decompositions into sequences > followed by a variation selector. > > In the case of compatibility decompositions, there already is no > expectation that neither the appearance nor the interpretation of the text > will change. With a decomposition mapping like "<font> 0069", the > decomposition is already indicating a typically different appearance. If > you decompose U+2139 to U+0069, you have already lost information about > appearance and interpretation. So it isn't that much of a stretch to assume > that any relevant variation sequences will also lose their interpretation. > > But I think it might make sense, in addition to the above textual fix, to > add a note to the standard to indicate that variation sequences preserve > their validity across *canonical* normalization forms, but that there is no > guarantee that variation sequences will remain valid for any compatibility > normalization. > > --Ken > > > 2012-11-24 8:12, Masatoshi Kimura wrote: > > > > > According to TUS v6.2 clause 16.4, > > > http://www.unicode.org/versions/Unicode6.2.0/ch16.pdf#page=15 > > >> The base character in a variation sequence is never a > > >> combining character or a decomposable character. > > > However, the following base characters appearing in > > > http://unicode.org/Public/6.2.0/ucd/StandardizedVariants.txt > > > have a decomposition mapping. > > > > There seems to be a contradiction here. “Decomposable character” is > > defined in clause 3.7 as follows: > > > > “A character that is equivalent to a sequence of one or more other > > characters, according to the decomposition mappings found in the Unicode > > Character Database, and those described in Section 3.12, Conjoining Jamo > > Behavior.” > > > > I suppose the intended meaning in clause 16.4, given its context, is to > > say that the base character is neither a combining character nor a > > character with a decomposition that contains a combining character. > > > > Yucca > > > > > > > >
