'Convert ``self`` into a new classifier by mapping a function over each
element produced by ``self``.
Parameters
relabeler : function[str -> str or None]
A function to apply to each unique value produced by ``self``.
Returns
relabeled : Classifier
A classifier produced by applying ``relabeler`` to each unique
value produced by ``self``.'

@string_classifiers_only
def relabel(self, relabeler):

    return Relabel(term=self, relabeler=relabeler)
