RE: ZWNJ/ZWJ and ligation of combining marks

From: Kent Karlsson (
Date: Thu Aug 28 2003 - 09:03:27 EDT

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    Peter Kirk wrote:
    > The Unicode standard, 4.0 section 15.2, specifies ZWJ and ZWNJ as the
    > characters to use for promoting or inhibiting ligatures. But the text
    > seems to assume that the characters being ligated are base
    > characters. A
    > problem arises when ZWJ or ZWNJ is inserted between combining
    > marks to
    > promote or inhibit ligation: as non-combining control
    > characters these
    > characters break the combining sequence, such that the following
    > combining mark forms a defective combining sequence whose
    > rendering is undefined.

    I have suggested that ZWJ and ZWNJ be made combining characters
    of class 0 (which would be permissibly stable), so that ZWJ and
    ZWNJ can occur between a base character and combining
    characters (needed for Khmer) or between Hebrew combining
    characters (that are in canonical order without the ZWJ/ZWNJ).
    Current use (between combining sequences) would fall under
    the special case of ZWJ/ZWNJ being at the end of a combining
    sequence (rather than after it).

                    /kent k

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