NIST test case 56

I don't think this is exactly an error, but it might be worth a note in 
the test case descriptions. It seems to me that NIST test case 56 will 
only cause a fatal error if the implementation supports the references 
property on attribute information items and the unparsed entities 
property on the document information item. Neither of these is required 
by the XInclude spec. Thus some processors may not encounter a fatal 
error when running this test case.

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Elliotte Rusty Harold