Re: Decomposed vs Composed accented characters

From: Philippe Verdy (verdy_p@wanadoo.fr)
Date: Sat Apr 08 2006 - 18:19:44 CST

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    From: "Kent Karlsson" <kent.karlsson14@comhem.se>
    > Otto Stolz wrote:
    >> The title of the ISO 88591 series contains the term "single-byte coded
    >> graphic character sets". The use of control functions for the coded
    >> representation of composite characters is prohibited by ISO 8859,
    >
    > This is mentioned because in ISO/IEC 646, the use of *control* codes,
    > more specifically backspace, was THE way of composing accented
    > characters. E.g. <A, backspace, (7-bit) circumflex> was supposed
    > to encode A WITH CIRCUMFLEX. The specification was incomplete,
    > and that aspect of ISO 646 never caught on, instead the national
    > variants did. Using backspace to encode composites is not allowed
    > in ISO/IEC 8859-x, it is likewise not allowed in ISO/IEC 10646.

    These are words that drive to the conclusion that ISO 8859 (any part), and ISO/IEC 10646 is not fully compatible with ISO 646.

    However, ISO 646 itself did NOT describe this use of BackSpace to compose characters with diacritics, and left Backspace only as an unspecified control (for use in application-dependant functions).

    Many (not all) ISO 646 national variants have used BackSpace to allow this, and some of them have been updated later to prohibit this use (this is the case of the last French variant of ISO646).

    You can see a (mostly complete) list of these (national or application-specific) variants and their use of Backspace on the "ISO 646" article of Wikipedia (French or English) which should list almost all the 7-bit character sets that are compatible with ISO 646 *and* were registered in the ISO-IR or IANA charsets repositories (the list does NOT include 7-bit charsets that are incompatible with ISO 646, even if they have a ISO-IR or IANA registration, because of their use of some invariant positions, but displays the characters that were assigned to variant positions, plus some invariant positions that were used in compositions)

    Philippe.

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