docs: def _make_valid_state_name(self, state_name):
          """Transform the input state_name into a valid state in XMLBIF.
          XMLBIF states must start with a letter an only contain letters,
          numbers and underscores.
          """
          s = str(state_name)
          s_fixed = pp.CharsNotIn(pp.alphanums + "_").setParseAction(pp.replaceWith("_")).transformString(s)
          if not s_fixed[0].isalpha():
              s_fixed = "state" + s_fixed
          return s_fixed