Microsoft XML Core Services (MSXML) 5.0 for Microsoft Office - XPath Reference

Boolean Functions

The XML Path Language (XPath) syntax supports Boolean functions that return strings or numbers, and can be used with comparison operators in filter patterns.

Boolean Functions

boolean Converts the argument to a Boolean.
false Returns false.
lang Returns true if the xml:lang attribute of the context node is the same as the argument string.
not Returns true if the argument is false, otherwise, false.
true Returns true.