Re: Defined Private Use was: SSP default ignorable characters

From: Peter Kirk (
Date: Wed Apr 28 2004 - 16:30:52 EDT

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    On 28/04/2004 12:23, Peter Constable wrote:

    >>While applications are of course not
    >>obliged to support the PUA, if they choose to do so there should be no
    >>expectation that they are party to any agreement. And so a group of
    >>users with a private agreement can reasonably assume that software
    >>supports the PUA in general supports their particular agreement.
    >Since there is not and cannot be any common specification for what it
    >means for an application to support the PUA, no assumptions can be made
    >by users about what an application does beyond what the application
    >vendor explicitly commits to. There is no rule anywhere that says that
    >an application must support whatever their customers might assume about
    >the PUA. The application vendor itself is a user of the Unicode
    >Standard, and is free to make it's own private assumptions.
    >(Of course, it may help their customers if they don't make too many
    Peter, I disagree with your first premise. There is a clear
    specification of what the Unicode standard expects as the default for
    support of the PUA. Each PUA has a default set of properties. All that
    they lack, apparently, are specific names and reference glyphs; but
    reference glyphs are not normative as the actual glyphs are always taken
    from the selected font, and character names are not exactly useful. If
    the defaults are taken as actual properties, that is a common
    specification for PUA characters which is not only able to exist but
    actually does exist. It is not exactly what I want it to be, but that is
    a separate issue.

    Of course it is then the decision of each implementer to decide whether
    to implement this part of the Unicode standard. But implementers can't
    claim that they cannot implement the PUA because they don't know what to do.

    Peter Kirk (personal) (work)

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