docs: def save_xml(self, doc, element):
          '''Save this execution context into an xml.dom.Element object.'''
          element.setAttributeNS(XSI_NS, XSI_NS_S + 'type', 'rtsExt:execution_context_ext')
          element.setAttributeNS(RTS_NS, RTS_NS_S + 'id', self.id)
          element.setAttributeNS(RTS_NS, RTS_NS_S + 'kind', self.kind)
          element.setAttributeNS(RTS_NS, RTS_NS_S + 'rate', str(self.rate))
          for p in self.participants:
              new_element = doc.createElementNS(RTS_NS,
                                                RTS_NS_S + 'Participants')
              p.save_xml(doc, new_element)
              element.appendChild(new_element)
          for p in self.properties:
              new_prop_element = doc.createElementNS(RTS_EXT_NS,
                                                     RTS_EXT_NS_S + 'Properties')
              properties_to_xml(new_prop_element, p, self.properties[p])
              element.appendChild(new_prop_element)