Re: Codepoint Differentiation

From: Asmus Freytag (
Date: Mon Feb 21 2005 - 18:02:45 CST

  • Next message: "Re: Codepoint Differentiation"

    > > Is there actually any problem with using Variation Selectors as-is to
    > > differentiate ...

    Doug already answered about the fact that only standardized sequences are valid
    and the only standardizer for sequences is the Unicode Consortium.

    Beyond that, variation selectors have another limitation: their only
    function is to identify variants - and that means variants with different
    GLYPH, not variants with different *behavior*.

    Variation selectors are designed to be ignorable for all processes that
    don't deal in rendering, and, they are also ignorable for low-fidelity
    rendering, i.e. rendering that does not support them (yes, I know, that's a
    bit circular).

    For distinctions in *sorting behavior*, a Combining Grapheme Joiner can
    often be used - but it is not intended to result in differences in display.

    The use of all of these special encoding crutches needs to be kept to a
    minimum. We all know cases where using a variation selector is preferable
    over adding a new character, since the differentiation is minute, not
    universally applicable or both. However, most text processes have to be
    designed to actively ignore them - and you have to be able to know, in
    advance, for which process they can (and must) be ignored.

    That means, you cannot arbitrarily use existing mechanisms to make
    distinctions that matter to algorithms that were designed to ignore these
    mechanisms. Therefore, for variation selectors, any non-glyphic
    distinctions are completely out of the picture.


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