boolean - XPath 编辑

XSLT/XPath Reference: XSLT elements, EXSLT functions, XPath functions, XPath axes

The boolean function evaluates an expression and returns true or false.

Syntax

boolean( expression )

expression: The expression to be evaluated. The expression can refer to numbers and node-sets as well as booleans.

Boolean true or false after evaluating expression.

A number evaluates to false if it is positive or negative zero or NaN. Otherwise, it evaluates true.
A node-set evaluates to true if it is non-empty.
A string evaluates to false if it an empty string. Otherwise, it evaluates to true.
An object of a type other than the four basic types is converted to a boolean in a way that is dependent on that type.