XML Signature recommends a standard means for specifying information content to be digitally signed and for representing the resulting digital signatures in XML.

One of the themes I heard consistently at YAPC was that every XML hacker who learned XPath said their life had changed. I played a little with XPath last night while writing the XML chapter for Cookbook 2ed, and I have to say--they're right. XPath is incredible.

XPath (XML Path Language) is a set of rules for addressing parts of an XML document. Using XPath, it is possible to address any point in an XML document without the need for embedding anchors and so on in the document.

The CPugXMLNode class wraps the xml_node class and provides additional XPath capability.

If you need to use XML with PHP, look no further than the awesome < phpXML > class written by Michael P. Mehl.

This document specifies a language, FXPath, for creating user-defined extension functions in XSLT stylesheets.

Demeter ideas are used in the XML domains described below. Demeter is an early generalization of XML that was developed years before XML.

The string-length function returns the number of characters in the string. You must use < as a substitute for < and > as a substitute for > .

Values of attributes can be used as selection criteria. Function normalize-space removes leading and trailing spaces and replaces sequences of whitespace characters by a single space.

Several paths can be combined with | separator.

This snippet is an improvement of the example in XPath Grouping 1. In our first example, we let the browser figure out how wide to make the columns.

Nonstandard XPath functions are supported in FormsPlayer through COM methods. An XML file maps namespace URIs to COM ProgIds to give access to these methods. [PDF]

The XML Recommendation [XML] specifies the syntax of a class of objects called XML documents. The Namespaces in XML Recommendation [XML-NS] specifies additional syntax and semantics for XML documents.

Function count() counts the number of selected elements.

The basic XPath syntax is similar to filesystem addressing. If the path starts with the slash / , then it represents an absolute path to the required element.

The star * selects all elements located by preceeding path.

Function name() returns name of the element, the starts-with function returns true if the first argument string starts with the second argument string, and the contains function returns true if the first argument string contains the second argument string.

In general, an XPath expression specifies a pattern that selects a set of XML nodes. XSLT templates then use those patterns when applying transformations. (XPointer, on the other hand, adds mechanisms for defining a point or a range, so that XPath expressions can be used for addressing.)

Uses an XPath language expression to search an XML document that is represented as a string variable.

The following example extracts all the elements named last, which contain the employee's last names, from the employeesimple.xml file, and displays the names: