

Some examples in a dataset may have a very long context that exceeds the maximum input length of the model. To deal with longer sequences, truncate only the context by setting truncation="only_second".
Next, map the start and end positions of the answer to the original context by setting
   return_offset_mapping=True.
With the mapping in hand, now you can find the start and end tokens of the answer. Use the [~tokenizers.Encoding.sequence_ids] method to
   find which part of the offset corresponds to the question and which corresponds to the context.