This class reacts on 'href' and 'src' attributes and is able to understand
the semantics of XHTML/WML/SMIL/SVG and all the rest of the languages that
use either XLink of the above attributes.
NOTE: this class is clearly a hack and is not future compatible, but
since many XML formats to date are not compatible with the XLink semantics
this is what we have to do to live in the bleeding edge. Once there will
be a way to remove this, that will be a happy day for XML and for Cocoon too.