There are two problems with IDS in Unicode 3.1:
1) The new unified ideographs U+20000 to U+2A6D6 need to be added to the
formal grammar of IDSes. The new compatibility ideographs
U+2F800 to U+2FA1D should be explicitly excluded from IDSes.
This is editorial.
2) TUS 3.0 says (p. 271):
# An implementation may render a valid [IDS] [...] by parsing the
# [IDS] and drawing the ideograph so described. In [that] case, the
# [IDS] should be treated as a ligature of the individual
# characters for purposes of hit testing, cursor movement,
# and other user interface operations.
Therefore, it would be useful to allow ZW(N)J in IDSes in order
to encourage or inhibit this ligaturing behavior. Adding
Joiner ::= U+200C | U+200D
and modifying the existing rule for IDS to allow these cases:
BinaryDescriptionOperator IDS Joiner IDS
TrinaryDescriptionOperator IDS Joiner IDS IDS
TrinaryDescriptionOperator IDS IDS Joiner IDS
TrinaryDescriptionOperator IDS Joiner IDS Joiner IDS
would do the trick.
This means that sequences like <U+2FF0, U+3400, U+200C, U+3401> which
were not IDSes before are now IDSes under the new definition.
-- There is / one art || John Cowan <firstname.lastname@example.org> no more / no less || http://www.reutershealth.com to do / all things || http://www.ccil.org/~cowan with art- / lessness \\ -- Piet Hein
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