| XPath defines 27 functions that may be called in expressions, including predicates. XSLT adds 9 functions to the XPath mix. You have already seen a number of these functions at work in previous examples in this book, such as name( ), string-length( ), and substring( ). Chapter 5 briefly documents all of the XPath 1.0 functions, including arguments. Similarly, Chapter 5 describes the XSLT 1.0 functions. XPath functions are divided into 4 types: Boolean, node-set, number, and string.  | Node tests such as text( ) and comment( ) look like functions but they are not really functions. Node tests simply test whether a given node matches a node type. |
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I'll demonstrate a number of functions in this chapter, but other chapters in this book will expose you to more examples of functions. For additional details on XPath functions, see Section 4 of the XPath specification. You can read more about XSLT functions in Sections 12 through 15 of the XSLT specification. | This is an introductory book and it does not provide exhaustive explanations of all of the XPath functions, though it will give you a chance to use many of them. John Simpson's XPath and XPointer (O'Reilly) explores XPath (and its derivative XPointer) in greater detail. Doug Tidwell's XSLT (O'Reilly), provides an excellent reference that demonstrates all these functions, as does Michael Kay's XSLT Programmer's Reference (Wrox). Another resource is Mulberry Technologies' XSLT and XPath Quick Reference at http://www.mulberrytech.com/quickref/XSLTquickref.pdf. |
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Table 5-1. XPath functions| XPath function signature | Type | Returns | Description |
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| boolean(object) | Boolean | Boolean | Converts the argument to a Boolean. | | ceiling(number) | Number | Number | Returns the smallest integer (closest to negative infinity) that is not less than the argument. | | concat(string, string, string*) | String | String | Returns a concatenation of two or more string arguments. | | contains(string, string) | String | Boolean | Returns true if the first argument contains the string in the second argument. | | count(node-set) | Node-set | Number | Returns the number of nodes in a node-set. | | false( ) | Boolean | Boolean | Returns false. | | floor(number) | Number | Number | Returns the largest integer (closest to positive infinity) that is not less than the argument. | | id(object) | Node-set | Node-set | Selects elements by unique ID. | | lang(string) | Boolean | Boolean | Returns true if the argument matches the context node's xml:lang value. | | last( ) | Node-set | Number | Returns the context size (the node position of the last node). | | local-name(node-set?) | Node-set | String | Returns the local part of an expanded QName (without a prefix). | | name(node-set?) | Node-set | String | Returns a QName. | | namespace-uri(node-set?) | Node-set | String | Returns a namespace URI. | | normalize-space(string?) | String | String | Returns a string with its whitespace normalized. | | not(boolean) | Boolean | Boolean | Returns true if the argument is false. | | number(object?) | Number | Number | Converts an object to a number. | | position( ) | Node-set | Number | Returns the context position (of the current node). | | round(number) | Number | Number | Returns an integer, rounded closest to the value of the argument. | | starts-with(string, string) | String | Boolean | Returns true if the first string starts with the second; otherwise it returns false. | | string(object?) | String | String | Converts an object into a string. | | string-length(string?) | String | Number | Returns the length of a string. | | substring(string, number, number?) | String | String | Returns a substring of the first argument, based on the starting position in the second argument, and the optional length in the third. | | substring-after(string, string) | String | String | Returns the substring of the first argument that follows the first occurrence of the second argument in the first. | | substring-before(string, string) | String | String | Returns the substring of the first argument that precedes the first occurrence of the second argument in the first. | | sum(node-set) | Number | Number | Returns a sum of nodes. | | translate(string, string, string) | String | String | Returns the first argument string with occurrences of characters in the second replaced by corresponding characters in the third. | | true( ) | Boolean | Boolean | Returns true. |
Table 5-2. XSLT functions| XSLT function signature | Returns | Description |
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| document(object, node-set?) | Node-set | Loads additional documents, allowing a transformation to have more than one input document. | | key(string, object) | Node-set | Applies the key in the first argument using the second argument. | | format-number(number, string, string?) | String | Converts a number to a string using the format pattern in the second argument and the decimal format identified by the third argument, if present. | | current( ) | Node-set | Returns the current node. | | unparsed-entity-uri(string) | String | Returns a URI for an unparsed entity. | | generate-id(node-set?) | String | Generates a unique ID for an element in the result tree. | | system-property(string) | Object | Returns an XSLT system property. | | element-available(string) | Boolean | Returns true if the named element is available. | | function-available(string) | Boolean | Returns true if the named function is available. |
| If you need even more functions, consider exploring the EXSLT extensions library, explained in Chapter 15. |
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