code: def _create_reference_value_options(self, keys, finished_keys):
          
          # a set of known reference_value_from_links
          set_of_reference_value_option_names = set()
          for key in keys:
              if key in finished_keys:
                  continue
              an_option = self.option_definitions[key]
              if an_option.reference_value_from:
  
                  fully_qualified_reference_name = '.'.join((
                      an_option.reference_value_from,
                      an_option.name
                  ))
                  if fully_qualified_reference_name in keys:
                      continue  # this referenced value has already been defined
                                # no need to repeat it - skip on to the next key
                  reference_option = an_option.copy()
                  reference_option.reference_value_from = None
                  reference_option.name = fully_qualified_reference_name
                  # wait, aren't we setting a fully qualified dotted name into
                  # the name field?  Yes, 'add_option' below sees that
                  # full pathname and does the right thing with it to ensure
                  # that the reference_option is created within the
                  # correct namespace
                  set_of_reference_value_option_names.add(
                      fully_qualified_reference_name
                  )
                  self.option_definitions.add_option(reference_option)
  
          for a_reference_value_option_name in set_of_reference_value_option_names:
              for x in range(a_reference_value_option_name.count('.')):
                  namespace_path = \
                      a_reference_value_option_name.rsplit('.', x + 1)[0]
                  self.option_definitions[namespace_path].ref_value_namespace()
  
          return set_of_reference_value_option_names
docs: this method steps through the option definitions looking for
          alt paths.  On finding one, it creates the 'reference_value_from' links
          within the option definitions and populates it with copied options.