Some time back there was an erratum to add intersect and except operators from XPath 2.0 to DFDL. I believe these were in use by the DFDL4S flavor of Daffodil, and so were added to DFDL v1.0.

Are these operators restricted to accept or to produce 0 or 1 node only,  or are they able to accept and produce lists of nodes that can then be counted with fn:count, for example? 

I guess I have lost track of the use-cases for these. The XPath 2.0 definition of these operators is of course fully general, accepting multiple node sequences, and producing multiple-node sequences. That would mean the ultimate result of these operators could be a sequence of more than one node, and that means it would have to be an argument to fn:count, fn:exists, .... not sure what other functions. They could never be the direct result-producing part of an expression.

Can someone point me at the use case for these again?