Re: Definition of case folding - where?

From: Mark Davis (
Date: Mon Sep 05 2005 - 11:05:26 CDT

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    In 3.13 Default Case Operations, it starts with the following paragraph.
    If you then look at section 4.2, it contains the references to the UCD
    defining the operations. (However, I agree that the text could be clearer.)

    > This section specifies the default operations for case conversion,
    case detection, and caseless
    > matching. For information about the data sources for case mapping,
    see Section 4.2,
    > Case—Normative. For a general discussion of case mapping operations,
    see Section 5.18,
    > Case Mappings.


    Jukka K. Korpela wrote:
    > 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 default_fold(C)."
    > 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 refer to UAX #21 Case Mappings, which has been superseded in Unicode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...

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