What is XPath?
XPath is a major element in the XSLT standard.
XPath can be used to navigate through elements and attributes in an XML document.
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XPath Path Expressions
XPath uses path expressions to select nodes or node-sets in an XML document.
These path expressions look very much like the path expressions you use with traditional computer file systems:
XPath Standard Functions
XPath includes over 200 built-in functions.
There are functions for string values, numeric values, booleans, date and time comparison, node manipulation, sequence manipulation, and much more.
Today XPath expressions can also be used in JavaScript, Java, XML Schema, PHP, Python, C and C++, and lots of other languages.
XPath is Used in XSLT
XPath is a major element in the XSLT standard.
With XPath knowledge you will be able to take great advantage of your XSLT knowledge.
XPath is a W3C Recommendation
XPath 1.0 became a W3C Recommendation on November 16, 1999.
XPath 2.0 became a W3C Recommendation on January 23, 2007.
XPath 3.0 became a W3C Recommendation on April 8, 2014.
XPath uses path expressions to select nodes or node-sets in an XML document. The node is selected by following a path or steps.
The XML Example Document
We will use the following XML document in the examples below.
Harry Potter
29.99
Learning XML
39.95
Selecting Nodes
XPath uses path expressions to select nodes in an XML document. The node is selected by following a path or steps. The most useful path expressions are listed below:
nodename | Selects all nodes with the name "nodename" |
/ | Selects from the root node |
// | Selects nodes in the document from the current node that match the selection no matter where they are |
. | Selects the current node |
.. | Selects the parent of the current node |
@ | Selects attributes |
In the table below we have listed some path expressions and the result of the expressions:
bookstore | Selects all nodes with the name "bookstore" |
/bookstore | Selects the root element bookstore Note: If the path starts with a slash [ / ] it always represents an absolute path to an element! |
bookstore/book | Selects all book elements that are children of bookstore |
//book | Selects all book elements no matter where they are in the document |
bookstore//book | Selects all book elements that are descendant of the bookstore element, no matter where they are under the bookstore element |
//@lang | Selects all attributes that are named lang |
Predicates
Predicates are used to find a specific node or a node that contains a specific value.
Predicates are always embedded in square brackets.
In the table below we have listed some path expressions with predicates and the result of the expressions:
/bookstore/book[1] | Selects the first book element that is the child of the bookstore element. Note: In IE 5,6,7,8,9 first node is[0], but according to W3C, it is [1]. To solve this problem in IE, set the SelectionLanguage to XPath: In JavaScript: xml.setProperty["SelectionLanguage","XPath"]; |
/bookstore/book[last[]] | Selects the last book element that is the child of the bookstore element |
/bookstore/book[last[]-1] | Selects the last but one book element that is the child of the bookstore element |
/bookstore/book[position[]35.00] | Selects all the book elements of the bookstore element that have a price element with a value greater than 35.00 |
/bookstore/book[price>35.00]/title | Selects all the title elements of the book elements of the bookstore element that have a price element with a value greater than 35.00 |
Selecting Unknown Nodes
XPath wildcards can be used to select unknown XML nodes.
* | Matches any element node |
@* | Matches any attribute node |
node[] | Matches any node of any kind |
In the table below we have listed some path expressions and the result of the expressions:
/bookstore/* | Selects all the child element nodes of the bookstore element |
//* | Selects all elements in the document |
//title[@*] | Selects all title elements which have at least one attribute of any kind |
Selecting Several Paths
By using the | operator in an XPath expression you can select several paths.
In the table below we have listed some path expressions and the result of the expressions:
//book/title | //book/price | Selects all the title AND price elements of all book elements |
//title | //price | Selects all the title AND price elements in the document |
/bookstore/book/title | //price | Selects all the title elements of the book element of the bookstore element AND all the price elements in the document |