XLink

XLink is a W3C specification that specifies ways to define links between various resources. It partially originated from the early TEI ideas on extended links and extended pointer syntax (later on, the extended pointer syntax ended up in the XPointer spec).

It is not used by the current Guidelines, though it may be plugged into a TEI extension, e.g. via Roma or Vesta, by means of something like the XLink.odd. It is used by e.g. the Scalable Vector Graphics and METS. Of course, (X)HTML links are non-conforming versions of XLink simple links.

W3C specifications

 * XLink 1.0 (Recommendation)
 * XLink 1.1 (Last Call Working Draft, as of 19:22, 2 November 2009 (EST)), which, a.o., makes @href:type optional
 * the errata

... of historical interest

 * comp.text.sgml posting by C.M. Sperberg-McQueen on the ideas behind extended links (1997)
 * single-page version of extended pointer tutorial by Lou Burnard (1997)

Other

 * Wikipedia entry