Re: Definitions

Date: Thu Nov 13 2003 - 04:56:31 EST

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    Quoting Chris Jacobs <>:

    > "The interpretation of private use characters (Co) as graphic characters or
    > not is determined by private agreement."
    > "The interpretation of private use characters (Co) as base characters or not
    > is determined by private agreement."
    > "The interpretation of Private Use characters (Co) as combining characters or
    > not is determined by private agreement. "
    > Is this just another way of saying that this is left undefined, or does it
    > imply that a conformant application should be able to detect if private
    > agreements exist?

    In my reading a bit of both. These properties for these characters are
    undefined by Unicode.

    As I see it the following behaviours would all be conformant:

    1. Your application uses these characters in accordance to a private agreement
    between other users of the protocol the application was built to support.

    2. Your application works with a protocol which has a rule against the use of
    private use characters (such a rule would be at a higher level than Unicode)
    and it throws and error in such cases (this is really a variant on the first
    possibility - essentially a private agreement that these characters are non-
    characters and should not occur).

    3. Your application has no "knowledge" of any private agreement. It treats
    private use characters as graphic non-combining characters, rendering them with
    an indicator of a unrenderable character ("box" shapes and question marks are
    common glyphs for use here, the Last Resort font offers a glyph which indicates
    that it is a private use character rather than any other unknown character)
    and/or passing them to the next processing step unchanged.

    4. Your application behaves as in the item above, but offers a mechanism to
    override this behaviour (particularly useful if it were a library rather than
    an application per se).

    It is not conformant to "fix" these characters by replacing them with other
    characters, though obviously a application like item 1 or 2 can do whatever
    operation it is meant to do with them.

    Jon Hanna
    *Thought provoking quote goes here*

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