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  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:

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))