XPointer

XPointer is a system for addressing components of XML-based Internet media. It is divided among four specifications: a "framework" that forms the basis for identifying XML fragments, a positional element addressing scheme, a scheme for namespaces, and a scheme for XPath-based addressing. XPointer Framework is a W3C recommendation since March 2003.

The XPointer language is designed to address structural aspects of XML, including text content and other information objects created as a result of parsing the document. Thus, it could be used to point to a section of a document highlighted by a user through a mouse drag action.

During development, and until 2016, XPointer was covered by a royalty-free technology patent held by Sun Microsystems.

Positional element addressing

The element() scheme introduces positional addressing of child elements. This is similar to a simple XPath address, but subsequent steps can only be numbers representing the position of a descendant relative to its branch on the tree.

For instance, given the following fragment:

<foobar id="foo">
  <bar/>
  <baz>
    <bom a="1"/>
  </baz>
  <bom a="2"/>
</foobar>

results as the following examples:

 xpointer(id("foo")) => foobar
 xpointer(/foobar/1) => bar
 xpointer(//bom) => bom (a=1), bom (a=2)
 element(/1/2/1) => bom (a=1) (/1 descend into first element (foobar),
                               /2 descend into second child element (baz),
                               /1 select first child element (bom))

See also

• URI fragment
• HTML
• HyTime
• Text Encoding Initiative Guidelines
• XML

External links

• XPointer Framework
• Namespacing
• Path based addressing
• XPointer patent terms and conditions
• Open source implementation (CognitiveWeb)
• GPL License .NET implementation (XInclude.NET) Archived 2015-06-18 at the Wayback Machine
• Method and system for implementing hypertext scroll attributes on Google Patents, expired 2016-02-01