The second and more interesting part is that before attempting to do any parsing in ruby, it calls the ragel parse method.
This method is implemented in C and uses the Ragel state machine compiler. Hopefully most of you are familiar with Ragel, since it was sort of made famous in the ruby community by Zed Shaw's use of it in the Mongrel HTTP parser, which was later used by thin, unicorn, and other ruby webservers. It was also used by _why as the scanner for Hpricot.