Patterns

A node matches a pattern if the node is member of the result of evaluating the pattern wrt. some context.
(Compare this with XPointer use of XPath.)

Typical structure:

pattern:		location path | ... | location path
location path:		/step/ ... // ... /step
step:		axis nodetest predicate

Example:

match="section/subsection|appendix//subsection"

matches subsection elements occuring either as child elements of section elements or as descendants of appendix elements.

• a pattern is a set of XPath location paths separated by | (union)
• the axes are restricted to child (default) and attribute (@)
• the location paths may start with id(..) or key(..)

(The whole XPath language is used for expressions later...)