The description of the XPath Level 1 expression language says the following about the case in which a wsf:Expression selects more than one node in the resource:

"In the event that there is more than one node which would match the XPath, the implementation SHOULD select or return the first node only. This allows simple implementations to avoid the overhead of checking the remainder of the resource document for a possible match."

The above "SHOULD" creates a number of interop problems, especially in the case of fragment Puts.

Proposal: s/SHOULD/MUST/