code: def AddXrefFrom(self, ref_kind, classobj, methodobj, offset):
          
          self.xreffrom[classobj].add((ref_kind, methodobj, offset))
docs: Creates a crossreference from this class.
          XrefFrom means, that the current class is called by another class.
  
          :param REF_TYPE ref_kind: type of call
          :param classobj: :class:`ClassAnalysis` object to link
          :param methodobj:
          :param offset: Offset in the methods bytecode, where the call happens
          :return: