3.2 / 4.3.1: {value contraint} in top-level attribute declaration s

In 3.2, the {value constraint} property of Attribute Declaration components
seems to allow a (value, absent) pair. This is supported by the property
correspondences for "attribute" element information items (4.3.1) directly
under "schema" where {value constraint}'s representation is:

	If there is a value attribute, then a pair consisting of the lexical
value of that attribute and absent, otherwise absent

What is the meaning of a {value contraint} that is a (value, absent) pair?

In this particular case, it seems the value of the "use" attribute is
ignored, but doesn't it default to "optional"?

James
--
James Tauber
jtauber@bowstreet.com
Director XML Technology
Bowstreet www.bowstreet.com