Nikita Popov 582a65b06f Implement full case mapping ...

Implement full case mapping according to SpecialCasing.txt and
also full case folding according to CaseFolding.txt (F). There
are a number of caveats:

* Only language-agnostic and unconditional full case mapping
  is implemented. The only language-agnostic conditional case
  mapping rule relates to Greek sigma in final position
  (Final_Sigma). Correctly handling this requires both arbitrary
  lookahead and lookbehind, which would require some larger
  changes to how the case mapping is implemented. This is a
  possible future extension.
* The only language-specific handling that is implemented is
  for Turkish dotted/undotted Is, if the ISO-8859-9 encoding
  is used. This matches the previous behavior and makes sure
  that no codepoints not supported by the encoding are
  produced. A future extension would be to also handle the
  Turkish mappings specified by SpecialCasing.txt based on
  the mbfl internal language.
* Full case folding is implemented, but case-insensitive mb_*
  operations continue to use simple case folding. The reason is
  that full case folding of the haystack string may change the
  position at which a match occurred. This would have to be
  mapped back into the position in the original string.
* mb_convert_case() exposes both the full and the simple case
  mapping / folding, where full is the default. The constants
  are:

   * MB_CASE_LOWER (used by mb_strtolower)
   * MB_CASE_UPPER (used by mb_strtolower)
   * MB_CASE_TITLE
   * MB_CASE_FOLD
   * MB_CASE_LOWER_SIMPLE
   * MB_CASE_UPPER_SIMPLE
   * MB_CASE_TITLE_SIMPLE
   * MB_CASE_FOLD_SIMPLE (used by case-insensitive operations)

2017-07-28 12:32:50 +02:00

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