Generic base characters (was: Hebrew generic base)

From: John Hudson (
Date: Thu Jul 12 2007 - 16:53:48 CDT

  • Next message: Kenneth Whistler: "RE: Hebrew generic base"

    Philippe Verdy wrote:

    > If you just consider the case of the cross base used in Lao, or the
    > underline base used in Lao, they are indeed easily confusable in
    > Latin/Greek/Cyrillic for the former (with letter x), and in Arabic (with the
    > shaddah).

    Yes, so document creators would be ill-advised to use those particular characters as
    generic bases in the context of those languages (note, however, not shaddah, tatweel
    (kashida), which is, by the way, sometimes used as a generic base for Arabic marks).

    The point is that the layout engine shouldn't be deciding which generic bases to allow for
    particular scripts or languages. It should allow all of them for any script, just as it
    allows the dotted circle. At the next level, font developers might decide not to support a
    particular generic base if it happens to be confuseable in the scripts and languages
    supported by the font, but even he might decide to leave the decision to the document creator.

    > We can't safely assume that generic bases will work in all scripts and all
    > languages, including those that are still unencoded but will use combining
    > diacritics...

    Work in what sense? The sense that matters to me is that layout engines should include the
    characters that may be used as generic bases in the same text runs as following combining
    marks, regardless of script or language. That's why the bases are *generic*. So what is
    the easiest way to implement this? Define a set of characters that may be used as generic
    bases, based on documentation of existing conventions, and specify that these should all
    be treated in the same way as the dotted circle base.

    If the UTC are interested in this idea, I can start defining such a set and gather
    feedback and requested additions from publishers, lexicographers, scholars, etc.

    John Hudson

    Tiro Typeworks
    Gulf Islands, BC
    We say our understanding measures how things are,
    and likewise our perception, since that is how we
    find our way around, but in fact these do not measure.
    They are measured.   -- Aristotle, Metaphysics

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