Den 2011-11-05 04:23, skrev "António Martins-Tuválkin" <tuval...@gmail.com>:
> I'm going through N4106 ( http://std.dkuug.dk/jtc1/sc2/wg2/docs/n4106.pdf ), ... I see the following characters being put forward for proposing to be encoded: 1ABB COMBINING PARENTHESES ABOVE 1ABC COMBINING DOUBLE PARENTHESES ABOVE 1ABD COMBINING PARENTHESES BELOW 1ABE COMBINING PARENTHESES OVERLAY Well, COMBINING DOUBLE PARENTHESES ABOVE seems to be the same as <COMBINING PARENTHESES ABOVE, COMBINING PARENTHESES ABOVE>. And COMBINING PARENTHESES OVERLAY seems to be just a tiny parenthesis before and a tiny parenthesis after; no need for a combining mark, especially one with a splitting behaviour. Otherwise, I think COMBINING ((DOUBLE)) PARENTHESES ABOVE/BELOW are an entirely new brand of characters in Unicode (if accepted as proposed). They are supposed to split (ok, we have split vowels in some Indic scripts, more on that below), but these split around *another combining mark*. So despite being given (as proposed) vanilla above/below mark properties, they do not "stack" the way such characters normally do, but is supposed to invoke an entirely new behaviour. Split vowels are not new, but they split around base characters (or more generally, around combining sequences), not around (a) combining character(s) only. Indeed, one can split these vowels into two characters (sometimes by canonical decomposition, when done right; sometime by cheating a bit and split into another character and the supposedly split vowel character but not interpreted as the second part of the decomposition; in principle one may need to cheat even more and use PUA characters in order to do this at the character level, but then that is really bad). That supposedly stacking combining marks *sometimes* (more a font dependence than a character dependence) don't stack but instead are laid out linearly is not new. But to *require* non-stacking behaviour for certain characters is new. So we have a combination of: 1. Splitting. (Normally only used for some Indic scripts). 2. Indeed splitting with no other characters to use for the decomposition, thus requiring the use of PUA characters, to stay compliant, for representing the result of the split at the character level. (This is entirely new, as far as I can tell.) 3. The split is entirely *within* the sequence of combining characters (except for COMBINING PARENTHESES OVERLAY, which behaves as split vowels normally do, but still with issue 2), not around the combining sequence including the base. (This is entirely new.) 4. Requiring (if at all supported) to use linear layout of combining characters instead of stacking. (This is entirely new.) This makes these proposed characters entirely unique in their display behaviour, IMO. This could be alleviated by encoding COMBINING BEGIN/END PARENTHESIS ABOVE/BELOW. That way the issues with split, as listed above, can be avoided. There is still the issue of requiring (when at all supported) linear layout instead of stacking. But at least that is a lesser concern. In summary, I'd propose replacing the four problematic proposed characters above with: COMBINING BEGIN PARENTHESES ABOVE (or LEFT) COMBINING END PARENTHESES ABOVE (or RIGHT) COMBINING BEGIN PARENTHESES BELOW (or LEFT) COMBINING END PARENTHESES BELOW (or RIGHT) BASELINE SMALL BEGIN PARENTHESES (or LEFT) BASELINE SMALL END PARENTHESES (or RIGHT) (or MODIFIER LETTER instead of BASELINE; the latter two are not combining) /Kent K