Re: Defined Private Use was: SSP default ignorable characters

From: Philippe Verdy (
Date: Wed Apr 28 2004 - 17:55:28 EDT

  • Next message: John Jenkins: "Re: Defined Private Use was: SSP default ignorable characters"

    From: "John Hudson" <>
    > Philippe Verdy wrote:
    > > Interesting point. This would be an argument for the developement (out of
    > > Unicode) of some standard technical solutions to exchange these private
    > > conventions on PUA usage, including exchange of character properties, etc...
    > >
    > > Why not then within fonts -- namely in Opentype tables for fonts built with
    > > these PUA assignments?
    > Fonts are collections of glyphs. It is important to keep this in mind when
    proposing that,
    > somehow, character properties be included in fonts.

    This is not so stupid: a font made for PUAs will also deliver at least a
    definition URI record. The actual character properties tables need not be
    present within the font itself.

    So just suppose that a XML schema is created to reference or embed various
    character properties data tables, and made accessible at a known URL or with a
    well-defined URN, then such XML document could be sufficient to describe
    completely what is in a private user agreement for PUAs.

    This means that this document URI can be inserted within the font (I'm quite
    sure that the OpenType format already has such meta-tags table, in which a URI
    could be inserted to access those properties).

    The private user agreement becomes explicit when a user tags its document with
    this URI. So the document becomes interchangeable even if it uses PUAs. And
    already today, the language tags could convey this URI within plain-text files
    containing those PUAs, or within standard XML files or within Word documents
    (using custom document meta-tags), or within HTML files (here also using <meta>

    This does not break what a font is made for: it is still a collection of glyphs
    and of glyph positioning and substituing tables. What this meta tag inserted
    into the font will indicate is that the font was made according to an explicit
    user agreement. Some fonts may be made that will work with several PUA
    agreements... by listing multiple URIs in them. The URI is then exactly like an
    interface signature.

    This would have an interest: if some PUA convention starts becoming popular, the
    private definitions files accessed from that URI will already constitute a
    viable experimentation for future characters to standardize.

    The same mechanism would also be used to tag Unicode versions or subsets
    supported in standard fonts...

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