docs: def parse(self, only_known = False):
          '''Ensure all sources are ready to be queried.
  
          Parses ``sys.argv`` with the contained ``argparse.ArgumentParser`` and
          sets ``parsed`` to True if ``only_known`` is False.  Once ``parsed`` is
          set to True, it is inadvisable to add more parameters (cf.
          ``add_parameter``).  Also, if ``parsed`` is not set to True, retrieving
          items (cf. ``__getitem__``) will result in a warning that values are
          being retrieved from an uparsed Parameters.
  
          **Arguments**
  
          :``only_known``: If True, do not error or fail when unknown parameters
                           are encountered.
  
                           .. note::
                               If ``only_known`` is True, the ``--help`` and
                               ``-h`` options on the command line (``sys.argv``)
                               will be ignored during parsing as it is unexpected
                               that these parameters' default behavior would be
                               desired at this stage of execution.
  
          '''
  
          self.parsed = not only_known or self.parsed
  
          logger.info('parsing parameters')
  
          logger.debug('sys.argv: %s', sys.argv)
  
          if only_known:
              args = [ _ for _ in copy.copy(sys.argv) if not re.match('-h|--help', _) ]
  
              self._group_parsers['default'].parse_known_args(args = args, namespace = self._argument_namespace)
          else:
              self._group_parsers['default'].parse_args(namespace = self._argument_namespace)