Re: Question about the replacement of Greek extended characters (u1F..) by equivalent Greek ones (u03..)

From: John Hudson (
Date: Thu Aug 23 2007 - 12:53:13 CDT

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    Ginette Beurton wrote:

    > I wonder about the drawbacks generated by the replacement of some of
    > the Greek extended characters by the Greek equivalent character when it
    > exist, for example : ( u1F71, u1F75, u1F77, u1F79, ...) replaced
    > respectively by u03CA, u03AE, U03AF, u03CC, ...

    > The question is that, in the Unicode standard, the Greek extended
    > characters are declared as equivalent to the Greek ones but the reverse
    > is not done.
    > For example, u03AF is not declared as an equivalent of u1F71. So the
    > relation between the 2 codes is not symmetric. Does that generate any
    > drawbacks ?

    The three-line equivalency symbol indicates canonical decomposition. This means that, for
    instance, U+1F71 canonically decomposes to U+03AC (note, not U+03AF): that the 'alpha with
    tonos' character is a fully legitimate way to encode the 'alpha with oxia' character, that
    they are identical, and that U+1F71 may be converted to U+03AC during text normalisation.

    Note also that U+03AC may itself be decomposed to the base + combining mark sequence
    <03B1, 0301>. U+0301 is the generic combining acute mark character.

    The only caution I would raise about using U+03AC and other Greek letters with tonos in
    place of the equivalent extended letters with oxia is that some font developers,
    erroneously in my opinion, make a visual distinction between the tonos mark and the oxia
    mark, e.g. by making the tonos mark more vertical. When the monotonic system was
    legislated in Greece, there was a brief fad for making strange tonos mark forms such as
    triangles, this confused many people and as a result not everyone realises that the tonos
    and oxia are, in fact, the same accent.

    So using U+03AC instead of U+1F71 may not get the visual result that you want in all
    fonts. Of course, performing normalisation decompositions of text may also result in a
    change in display with those fonts.

    John Hudson

    Tiro Typeworks
    Gulf Islands, BC
    Do not begin to paddle unless you intend always to paddle.
              - St Jean de BrΓ©beuf, instructions for missionaries, 1637

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