Definition of case folding - where?

From: Jukka K. Korpela (
Date: Mon Sep 05 2005 - 09:28:54 CDT

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    I'm unable to find the definition of case folding in the Unicode standard.
    Chapter 3 says (in 3.13):
    "The full case folding of a character C is referred to as
    But this is just a notation. The files SpecialCasing.txt and
    UnicodeData.txt define full case mappings to lowercase, uppercase, and
    titlecase. So what's full case _folding_?

    It seems that the intended meaning is that full case folding is canonical
    decomposition followed by full case mapping to lowercase. That's at least
    the idea I get from looking at the specific foldings at
    But where is the definition?

    Is it possible that the definition was accidentally lost in the
    reorganization of the standard? Several documents, like the charts at the
    URL mentioned above as well as the Unicode database file CaseFolding.txt,
    refer to UAX #21 Case Mappings, which has been superseded in Unicode
    version 4.0, so I thought that something was accidentally dropped when
    incorporating UAX #21 into the standard. But I'm unable to find a
    definition of case folding in UAX #21 either...

    Jukka "Yucca" Korpela,

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