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3.4. XPath Datatypes

An XPath expression returns one of four datatypes:

node-set
Represents a set of nodes. The set can be empty, or it can contain any number of nodes.

boolean
Represents the value true or false. Be aware that the true or false strings have no special meaning or value in XPath; see Section 4.2.1.2, "Boolean examples" in Chapter 4, "Branching and Control Elements" for a more detailed discussion of boolean values.

number
Represents a floating-point number. All numbers in XPath and XSLT are implemented as floating-point numbers; the integer (or int) datatype does not exist in XPath and XSLT. Specifically, all numbers are implemented as IEEE 754 floating-point numbers, the same standard used by the Java float and double primitive types. In addition to ordinary numbers, there are five special values for numbers: positive and negative infinity, positive and negative zero, and NaN, the special symbol for anything that is not a number.

string
Represents zero or more characters, as defined in the XML specification.

These datatypes are usually simple, and with the exception of node-sets, converting between types is usually straightforward. We won't discuss these datatypes in any more detail here; instead, we'll discuss datatypes and conversions as we need them to do specific tasks.



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