4. Document path: XPath

XPath is a specification for describing an XML document tree traversal model using a path expression. This technique exploits the genealogical relationships existing between the nodes that make up the document to select the set of nodes reached by following all paths conforming to the given model. This language is used in many tools in the XML galaxy, notably XSL and XSLT, to locate a specific node or set of nodes in order to associate them with a presentation or transformation. It is also used in XPointer and XLink to identify document fragments and point to a specific target in a document. Finally, in XML query languages such as XQuery, it is used to locate a specific node or set of nodes for post-processing.