In a fairly wild environment (http://www.thaivisa.com/forum/topic/730564-new-front-end-to-ri-dictionary-alpha), I encountered the following question:
"If you search for ก* do you expect to return words such as เก่ง and ไก่?" Now, as a regular expression, in UTS#18 'Unicode Regular Expressions' Version 13 (dated 2008, superseded in 2012), RL3.5 comes pretty close to this with ranges tailored for collation. The pattern [\u0E01-\u0E02]* would match both those words. To be precise, one would use a search for [ก-ไก]*. RL3.5 has been with withdrawn because of difficulties, though I can't say that I see it as a major difficulty that at least one of [A-z] and [a-Z] is empty. Even POSIX is aware of that little issue. Turning to fully collation-based definition of searches, UTS#10 Unicode Collation Algorithm's definition DS2 comes closest to answering the question for the UTC. DS2 reads: DS2. The pattern string P has a match at Q[s,e] according to collation C if C generates the same sort key for P as for Q[s,e], and the offsets s and e meet the boundary condition B. One can also say P has a match in Q according to C. It's a soft job to create sequences of codepoints P starting with U+0E01 THAI CHARACTER KO KAI that are tertiary matches for เก่ง and ไก่ under both DUCET and the CLDR collations for Thai. Can I therefore say that the two strings match the pattern ก* according to these collations? (A pattern P for ไก่ <U+0E44 THAI CHARACTER SARA AI MAIMALAI, U+0E01 THAI CHARACTER KO KAI, U+0E48 THAI CHARACTER MAI EK> is P = <U+0E01, U+0E34F COMBINING GRAPHEME JOINER, U+0E44, U+0E48>.) Disturbingly, another possible answer is that there is no match for <U+0E01 THAI CHARACTER KO KAI> in either string because it only occurs in the legacy/extended grapheme cluster <U+0E01, U+0E48>. Richard. _______________________________________________ Unicode mailing list [email protected] http://unicode.org/mailman/listinfo/unicode
