code: def add_description(self, type_p, v_box_value, extra_config_value):
          
          if not isinstance(type_p, VirtualSystemDescriptionType):
              raise TypeError("type_p can only be an instance of type VirtualSystemDescriptionType")
          if not isinstance(v_box_value, basestring):
              raise TypeError("v_box_value can only be an instance of type basestring")
          if not isinstance(extra_config_value, basestring):
              raise TypeError("extra_config_value can only be an instance of type basestring")
          self._call("addDescription",
                       in_p=[type_p, v_box_value, extra_config_value])
docs: This method adds an additional description entry to the stack of already
          available descriptions for this virtual system. This is handy for writing
          values which aren't directly supported by VirtualBox. One example would
          be the License type of :py:class:`VirtualSystemDescriptionType` .
  
          in type_p of type :class:`VirtualSystemDescriptionType`
  
          in v_box_value of type str
  
          in extra_config_value of type str