    def _embed_spans(
        self,
        sequence_tensor: torch.FloatTensor,
        span_indices: torch.LongTensor,
        sequence_mask: torch.BoolTensor = None,
        span_indices_mask: torch.BoolTensor = None,
    ) -> torch.Tensor:
        """
        Returns the span embeddings computed in many different ways.
        """
        raise NotImplementedError
Returns the span embeddings computed in many different ways.
allennlp/modules/span_extractors/span_extractor_with_span_width_embedding.py