RNNs with two consecutive inputs). In this context, a segment is a number of consecutive tokens (for instance 512) that
may span across multiple documents, and segments are fed in order to the model.
Basically, the hidden states of the previous segment are concatenated to the current input to compute the attention
scores. This allows the model to pay attention to information that was in the previous segment as well as the current
one. By stacking multiple attention layers, the receptive field can be increased to multiple previous segments.
This changes the positional embeddings to positional relative embeddings (as the regular positional embeddings would
give the same results in the current input and the current hidden state at a given position) and needs to make some
adjustments in the way attention scores are computed.
