Any element can be a link
XLink elements are identified by an xlink:type
attribute with
one of these six values:
simple
extended
locator
arc
resource
title
Linking elements are identified by an xlink:type
attribute with
one of these two values:
simple
extended
Each
linking element contains an xlink:href
attribute whose
value is the URI of the resource being linked to.
An xmlns:xlink
attribute associates the xlink
prefix with the http://www.w3.org/1999/xlink namespace.