XML Pocket Reference, Second Edition

XPath

XPath is a recommendation of the World Wide Web Consortium (W3C) for locating nodes in an XML document tree. XPath is not designed to be used alone but in conjunction with other tools, such as XSLT or XPointer. These tools use XPath intensively and extend it for their own needs through new functions and new basic types.

XPath provides a syntax for locating a node in an XML document. It takes its inspiration from the syntax used to denote paths in filesystems such as Unix. This node, often called the context node, depends on the context of the XPath expression. For example, the context of an XSLT expression found in an xsl:template match="para" template will be the selected para element (recall that XSLT templates use XPath expressions). This node can be compared to a Unix shell’s current directory.

Given our earlier XML examples, it is possible to write the following expressions:

chapter

Selects the chapter element descendants of the context node

chapter/para

Selects the para element descendants of the chapter element children of the context node

../chapter

Selects the chapter element descendants of the parent of the context node

./chapter

Selects the chapter element descendants of the context node

*

Selects all element children of the context node

*/para

Selects the para grandchildren of the context node

.//para

Selects the para element descendants (children, children of children, etc.) of the context node

/para

Selects the para element children of the document root element ...