Set difference and intersection
These operators were introduced in XPath 2.0.
The expression E1 except E2 selects all nodes that are in E1 unless
they are also in E2. Both expressions must return sequences of nodes. The results
are returned in document order. For example, @* except @note returns all attributes
except the note attribute.
The expression E1 intersect E2 selects all nodes that are in both E1 and
 E2. Both expressions must return sequences of nodes. The results
are returned in document order. For example, preceding::fig intersect ancestor::chapter//fig 
returns all preceding fig elements within the current chapter.