(Captured en-passant during a WG telcon)

There are a number of restrictions on patterns that don't really have any good justification. This was an area we left largely untouched in 2.0 except where we automatically inherited changes being made to XPath expressions.

Constructs that would often be useful in patterns include:

* parentheses:  (//title)[1]

* union in a step:  (chapter|appendix)/title

* anchoring the pattern to a specific document:

       $lookup-doc//entry
       doc('lookup.xml')//entry

* matching any node that is a member of a preselected node-set 

       $preselection

* use of "." with a predicate:

       .[f:is-special(.)]

All of these can currently be expressed, but often rather inelegantly; the 4th case above, for example, is match="node()[. intersect $preselection]".