Re: What is the principle?

From: Doug Ewell (
Date: Wed Mar 31 2004 - 11:08:50 EST

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    Peter Kirk <peterkirk at qaya dot org> wrote:

    >> Which I assume means: "it's wrong for Unicode to make ANY property
    >> pronouncements for ANY PUA characters, since that defines them, and
    >> removes the P from the Use."
    > This is of course a principle which they have already broken, as they
    > have defined "default" properties for all of them. Although in
    > principle people can implement non-default properties, no one has, as
    > far as I know. The result is that in practice the P has been removed
    > from the PUA and it has been restricted to LTR base characters.

    Unicode allows the properties of the PUA code points, unlike all others,
    to be customized by the end user. I've done so myself, on the Web page
    I mentioned. Characters are classified as General Category Lo, Nd, or
    No, and the digits have numeric values. Although all are still LTR base
    characters, there's no reason they had to be (except that that's how my
    script works); for Tengwar there would be both RTL digits and combining

    The perception that no-one has yet implemented custom PUA properties
    does not mean that doing so is prohibited or unworkable, any more than
    the shortage of widely available rendering engines for the Tibetan and
    Khmer encoding models implies that those models are unworkable.

    Failure to see this distinction, between (a) what Unicode allows and
    prohibits and (b) what software products do and do not support, is doing
    more to convince us of the hardness of Peter's head than anything else.

    -Doug Ewell
     Fullerton, California

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