e.g. "this is how machine-generated parsers know to skip blanks and
comments"
The run time implementation could be better; we don't really want to
just discard trivia because it's useful for e.g. doc comments and the
like. BUT for now this is fine.
There was a bug in the way that I was converting regular expressions
to NFAs. I'm still not entirely sure what was going on, but I
re-visited the construction and made it follow the literature more
closely and it fixed the problem.
