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Section 3.2 talks about raising error XPDY0050 if a path starts with / and // and the root node above the context node is not a document node. XPDY0050 has to do with the treat expression. I understand that these operators act like a treat expression under the covers. However, I think it is going to be very hard to explain to users why they are getting an error about a treat expression when they don't even have a treat expression in their query. At the very least, the error message for XPDY0050 should be modified to add an explanation for this alternate scenario where it is raised.
Thanks, Priscilla. The descriptive message for error XPDY0050 has been modified according to your suggestion. Regards, Don Chamberlin (for the Query Working Group)