docs: def _get_rc_strings(cls):
          """
          Recursive method to get the base strings in the rcParams dictionary.
  
          This method takes the :attr:`_rcparams_string` attribute from the given
          `class` and combines it with the :attr:`_rcparams_string` attributes
          from the base classes.
          The returned frozenset can be used as base strings for the
          :meth:`psyplot.config.rcsetup.RcParams.find_and_replace` method.
  
          Returns
          -------
          list
              The first entry is the :attr:`_rcparams_string` of this class,
              the following the :attr:`_rcparams_string` attributes of the
              base classes according to the method resolution order of this
              class"""
          return list(unique_everseen(chain(
              *map(lambda base: getattr(base, '_rcparams_string', []),
                   cls.__mro__))))