XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (495 page)

In patterns, the
|
operator can be used only at the top level. XPath 2.0 allows expressions such as
(chap|appendix)/title
, but this is not a valid pattern. The required effect can be achieved by writing
chap/title|appendix/title
or, if you prefer,
title[parent::chap|parent:: appendix]
.

Examples

Construct	Meaning
TITLE	TITLE is a PathPattern , so it is also a Pattern .
preface|chapter| appendix	A node matches this pattern if it is a element, a element, or an element.
/|*	A node matches this pattern if it is either a document node or an element node.

PathPattern

A
PathPattern
states conditions that a node must satisfy based on its name, its node kind, its position relative to other nodes, and/or its ID and key values.

This construct is a subset of the
PathExpr
construct in the XPath grammar.

Syntax

Expression	Syntax
PathPattern	RelativePathPattern | / RelativePathPattern? | // RelativePathPattern | IdKeyPattern (( / | // )RelativePathPattern) ?