Re: [hebrew] Re: Hebrew composition model, with cantillation marks

From: Philippe Verdy (verdy_p@wanadoo.fr)
Date: Tue Nov 04 2003 - 09:54:26 EST

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    From: "Peter Kirk" <peterkirk@qaya.org>
    > The only issue is the
    > medial meteg, which can be solved most simply by defining a new medial
    > meteg character (or variation selector wiith meteg) which always
    > combines with an adjacent hataf vowel.

    According to Chapter 15 of the Unicode Standard:

        A variation sequence, which always consists of a base
        character followed by the variation selector, may be specified
        as part of the Unicode Standard. That sequence is referred to
        as a variant of the base character. The variation selector affects
        only the appearance of the base character, and only in the
        variation sequences defined in this Standard. The variation
        selector is not used as a general code extension mechanism.

    In other words, variation selectors are combining characters of combining
    class 0, added after a base character (non combining, class 0). It occurs in
    encoded sequences like <BASE, VS> which may then be followed by other
    combining characters in any combining class.

    This is confirmed later:

        The base character in a variation sequence is never a combining
        character or a decomposable character. The variation selectors
        themselves are combining marks of combining class 0 and are
        default ignorable characters. Thus, if the variation sequence is
        not supported, the variation selector should be invisible and
        ignored.

    So the standard variation selectors cannot be used to create a variant of
    meteg, because meteg is neither a base character, nor of combining class 0.

    All that can be done is to create a new variation selector for combining
    characters. It could be created:
        - either within a new generic set of variation selectors for combining
    characters (noted CVSn here) to produce sequences like <HEBREW POINT
    METEG><CVSn>;
        - or as Hebrew specific variation selectors for Hebrew combining
    characters (noted HVSn here); this would produce sequences like <HEBREW
    POINT METEG><HEBREW HVSn> which should be treated at <HEBREW POINT METEG> by
    renderers or collators that do not implement this variation selector.

    In either case, such types of variation selector sequences needed to
    override the rendered position of the previous combining character should be
    allowed only for registered sequences, like with other base characters with
    known variants.



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