| operator was available in XPath 1.0; the keyword
added in XPath 2.0 as a synonym, because it is familiar to SQL users.
E1 union E2 selects all nodes that are in either
E2 or both. Both expressions must return sequences of nodes. The results
are returned in document order. For example,
/book/(chapter | appendix)/sections returns
section elements within a
appendix of the