  NLP is deeply intertwined with the formal study of language, both
conceptually and historically. Arguably, this connection goes all the way back
to Chomsky's Syntactic Structures in 1957. It also still holds true today, with
a strand of recent works building formal analysis of modern neural networks
methods in terms of formal languages. In this document, I aim to explain
background about formal languages as they relate to this recent work. I will by
necessity ignore large parts of the rich history of this field, instead
focusing on concepts connecting to modern deep learning-based NLP.
