code: def registerViewType(self, cls, window=None):
          
          if ( not cls in self._viewTypes ):
              self._viewTypes.append(cls)
              
              if ( window ):
                  cls.registerToWindow(window)
docs: Registers the inputed widget class as a potential view class.  If the \
          optional window argument is supplied, then the registerToWindow method \
          will be called for the class.
          
          :param          cls     | <subclass of XView>
                          window  | <QMainWindow> || <QDialog> || None