XML in a Nutshell, 3rd Edition

Data Types

Each XPath expression evaluates to one of four types:

Boolean

A binary value that is either true or false. In XPath, Booleans are most commonly produced by using the comparison operators =, !=, <, >, <=, and >=. Multiple conditions can be combined using the and and or operators, which have their usual meaning in logic (e.g., 3>2 or 2>1 is true). XPath does not offer Boolean literals. However, the true( ) and false() functions fill that need.

Number

All numbers in XPath are IEEE 754-compliant, 64-bit floating-point numbers. This is the same as the double type in Java. Numbers range from 4.94065645841246544e-324d to 1.79769313486231570e+308d, and are either positive or negative. Numbers also include the special values Inf (positive infinity), -Inf (negative infinity), and NaN (not a number), which is used for the results of illegal operations, such as dividing by zero. XPath provides all the customary operators for working with numbers, including:

+

Addition

-

Subtraction; however, this operator should always be surrounded by whitespace to avoid accidental misinterpretation as part of an XML name

*

Multiplication

div

Division

mod

Taking the remainder

String

Sequence of zero or more Unicode characters. String literals are enclosed in either single or double quotes, as convenient. Unlike Java, XPath does not allow strings to be concatenated with the plus sign. However, the concat( ) function serves this purpose.

Node-set

Collection of zero or more nodes from an XML document. Location ...