code: def add_metadata_comments(self, d, metadata):
          
  
          if len(metadata) > 2:
              string_pairs = metadata[1:-1]  # get all metadata pairs
              for sp in string_pairs:
                  # get the raw metadata key
  
                  if isinstance(sp.children[0], Token):
                      token = sp.children[0]
                      assert token.type == "UNQUOTED_STRING"
                      key = token.value
                  else:
                      # quoted string (double or single)
                      token = sp.children[0].children[0]
                      key = token.value
  
                  # clean it to match the dict key
                  key = self._mapfile_todict.clean_string(key).lower()
                  assert key in d.keys()
                  key_comments = self.get_comments(sp.meta)
                  d["__comments__"][key] = key_comments
  
          return d
docs: Any duplicate keys will be replaced with the last duplicate along with comments