def tag(self, nerdoc):
        """Tag the given document.
        Parameters
        ----------
        nerdoc: estnltk.estner.Document
            The document to be tagged.

        Returns
        -------
        labels: list of lists of str
            Predicted token Labels for each sentence in the document
        """

        labels = []
        for snt in nerdoc.sentences:
            xseq = [t.feature_list() for t in snt]
            yseq = self.tagger.tag(xseq)
            labels.append(yseq)
        return labels