Learning XML, 2nd Edition

XPointer

Closely related to XPath is the XML Pointer Language (XPointer). It uses XPath expressions to find points inside external parsed entities, as an extension to uniform resource identifiers (URIs). It could be used, for example, to create a link from one document to an element inside any other.

Originally designed as a component of the XML Linking Language (XLink), XPointer has become an important fragment identifier syntax in its own right. The XPointer Framework became a recommendation in 2003 along with the XPointer element( ) Scheme (allowing basic addressing of elements) and the XPointer xmlns( ) Scheme (incorporating namespaces). The xpointer( ) scheme itself is stuck at Working Draft, getting no further development.

An XPointer instance, which I’ll just call an xpointer, works much like the fragment identifier in HTML (the part of a URL you sometimes see on the right side of a hash symbol). It’s much more versatile than HTML’s mechanism, however, as it can refer to any element or point inside text, not just to an anchor element (<a name="..."/>). By virtue of XPath, it has a few advantages over HTML fragment identifiers:

• You can create a link to the target element itself, rather than to a proxy element (e.g., <a name="foo"/>.

• You don’t need to have anchors in the target document. You’re free to link to any region in any document, whether the author knows about it or not.

• The XPath language is flexible enough to reach any node in the target document.

XPointer actually goes ...