ZWNJ/ZWJ and ligation of combining marks

From: Peter Kirk (
Date: Tue Aug 26 2003 - 13:09:14 EDT

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    This is an issue which has come up on the Unicode Hebrew list but has
    not been resolved there...

    There is a requirement in some cases, depending on the typographical
    convention in use, to form a ligature between the combining marks U+05BD
    HEBREW POINT METEG and any one of the three "hataf" vowel points U+05B1,
    U+05B2 and U+05B3. But there are also some exceptions i.e. cases in
    which the ligature should not be formed when the default is for it to be
    formed, and possibly cases when it should be formed when by default it
    is not to be formed.

    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

    An alternative that has been suggested has been to use CGJ between the
    combining marks. This has the advantage that CGJ is itself a combining
    mark and so does not break the combining sequence; but the disadvantage
    that this is one character, not two, and so cannot be used separately to
    promote or inhibit ligation. The more serious problem is that this use
    does not accord with the defined use of CGJ which is explicitly not to
    affect ligation.

    Can anyone on this list advise what should be done in this case?

    Peter Kirk (personal) (work)

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