A given node matches a given pattern if:

the node is member of the result of evaluating the pattern with respect to some context.

Operationally (and intuitively), a pattern matching is probably best evaluated backwards (from right to left).

Recall the structure of XPath node-set expressions:

• a pattern is a set of XPath location paths separated by | (union)
• restrictions: only the child (default) and attribute (@) axes are allowed here
• extensions: the location paths may start with id(..) or key(..)

A simple example is:

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

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

These figures illustrate the pattern matching mechanism.

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