The scoring is based on the top three words on the stack and the first word of the buffer, and the input to the MLP includes the BiLSTM vectors for these words as well as their leftmost and rightmost dependents (up to 12 words in total).
one of the most striking results, however, is that both parsers improve their accuracy on longer sentences, with some models for some languages in fact being more accurate on medium-length sentences than on shorter sentences.