Comparing lists to singletons

For the purpose of XML Schema identity constraints (for example key/keyref),
is the NMTOKENS value "x" equal to the NMTOKEN value "x"?

It depends on the definition of "equal" in XML Schema Part 2 section 4.2.1.
But the definitions there don't shed much light: they discuss union types
but not list types. It comes down to whether a sequence whose only item is
the string "x" is the same value (=value-space member) as the string "x",
and I don't see a statement on that anywhere.

The published test results (e.g. idc_NMTOKENS_Name.xml) show the result as
not equal, but with XSV and Xerces showing equal.

Michael Kay
http://www.saxonica.com/