Go to standardXPath function: boolean boolean (object)
Standard excerpt:
The boolean function converts its argument to a boolean as follows: a number is true if and only if it is neither positive
or negative zero nor NaN, a node-set is true if and only if it is non-empty, a string is true if and only if its length is
non-zero 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
Examples (xslt:xml): Overview
46:2
Interactive xlab: [number functions] [xsl:value-of] [xsl:template]