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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def tag_labels(self):
 """Tag named entity labels in the ``words`` layer."""

        if not self.is_tagged(ANALYSIS):
            self.tag_analysis()
        if self.__ner_tagger is None:
            self.__ner_tagger = load_default_ner_tagger()
        self.__ner_tagger.tag_document(self)
        return self