This class holds the specification of a reference used to validate against.
The information structure is consistent with the 'references.xsd', so that
the elements of the 'references.xml' can be represented. A reference is
specified through its name and the characteristics: XSD:QName or a XSD:IDREF
reference and located as attribute or as sub element. There are possibly also
the allowed types of the referenced elements. The special field marks it for
additional hard coded handling. The number allows an easy look up in the
corresponding bachelor thesis.