code: def set_error(self, msg, runSet=None):
          
          self.xml_header.set('error', msg if msg else 'unknown error')
          if runSet:
              runSet.xml.set('error', msg if msg else 'unknown error')
docs: Mark the benchmark as erroneous, e.g., because the benchmarking tool crashed.
          The message is intended as explanation for the user.