Constructing the Predicate Portion of a Location Step

The final possible component of an XPath location step, called the predicate, provides a further, finer-grained filter to select among the node(s) located by the node-test and axis. The basic form of a predicate is:

[something operator somevalue]

where:

• the square brackets, [ and ], are required;
• something may be either a further location step, relative to the nodes matched so far by the node-test and axis, or a built-in XPath function;
• operator is one of several Boolean operators, such as an equals sign or "!=" for a "does not equal" condition; and
• somevalue is the value to which you want to compare something.

For instance:

[position() = 1]

locates the first matching node in document order, while:

[attribute::empid != "73519"]

locates the subset of the matching node-set at that point which includes any nodes with an empid attribute whose string value does not equal "73519".

Note   Be careful when using the "<" and ">" operators in your XPath expressions. Because these characters are significant in markup, you will typically have to escape them using the < and > entity references. For example:

[attribute::empid <= "69999"]

says to select all nodes with an empid attribute whose value is <= (less than or equal to) "69999".

White space between the terms of a predicate is not significant. That is:

[position() = 1]

and

[position()=1]

function identically.

See Also

Filtering XML Data Using XPath Predicates