String.

Use string functions to test substring values, concatenate strings, or translate strings into other strings. The following XPath query predicate determines if an employee’s full name is equal to the concatenation of last name and first name:

Numeric.

Use numeric functions with element and attribute values. Numeric functions operate on numbers and return integers. For example, the following XPath query predicate rounds discount and tests if the result is greater than 15:

Boolean.

Boolean functions return either true or false. Use them to test elements, check the language attribute, or force a true or false result. For example, a string is true if the string value is greater than zero: