Reserved and Unassigned (was: Re: Wanted: synonyms for Age)

From: Kenneth Whistler (kenw@sybase.com)
Date: Fri Aug 07 2009 - 15:31:38 CDT

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    Karl Williamson asked:

    > I forgot to include the public list as a cc to this, which I am now
    > doing, but perhaps it is better, as I realize that I'm confused about
    > what reserved means. I thought from NamesList.txt that reserved
    > characters were unassigned ones that were never going to be assigned
    > because of some constraint on them, such as being place-holders. Like
    > the following:
    >
    > 1D51D <reserved>
    > x (black-letter capital z - 2128)
    >
    > where the code points around it are assigned, but this one essentially
    > duplicates 2128, and so is skipped.

    No. "Reserved code point" is simply a synonym for "unassigned
    code point". The label "<reserved>" in the Unicode names list is
    simply a convention for making a code point as reserved
    (or unassigned). What it is "reserved" for is possible future
    encoding. The reason that particular label was chosen was
    because it harmonized with longstanding practice in SC2
    standards, including ISO/IEC 10646.

    > But in looking at extracted/DerivedGeneralCategory.txt, it appears that
    > reserved is any Cn code point that isn't a non-character.

    Yep.

    See also Table 2-3, Types of Code Point, on p. 27 of TUS 5.0.

    --Ken

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