One of my favorite quotes about parsing is the title of
\link{http://tratt.net/laurie/blog/entries/parsing_the_solved_problem_that_isnt|a blog post by Laurence Tratt},
who referred to parsing as, "The Solved Problem That Isn't."
Parsing is tricky and weird and non-intuitive, and yet it seems
like it should be a simple task: you take text, you put it into

