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In section 4.2.1.1, the first 2 bullet points list restrictions on the xpath expression. I thought that, in the 1st F2F in Redmond, we agreed to remove these restrictions but that seems to have gotten lost. Couldn't find it in the minutes. For example, why restrict the union operator. Using this operator will not necessarily result in more than one result node. I believe we discussed moving some of these restrictions to "guidelines" or "best practices."
Currently the spec adds restrictions on the xpath expression in order to create a profile of the xpointer() scheme used to encode a fragment identifier. We have already decided not to use the xpointer() scheme. Proposal: resolve this as "won't fix" Once we decide on the new scheme (such as xpath1 scheme), we can then decide what restrictions to add on that specific scheme.
I think this should remain in its current state. As you point out, once we decide on the new scheme (4636, which 5133 is dependent upon) then we will deal with this one. 5133 will prompt us to have the right discussion at the right time (when 4636 is fixed).
Proposal: Resolve this bug as "won't fix". Reasons: We have consensus on 4636 to define our own scheme that fits into the xpointer framework. The current bug deals with restrictions on the xpath used in the xpointer() scheme. Since we have decided to not use the xpointer() scheme, this bug is no longer relevant.