Starting with the second definition of the function non-triv-pat-p (the real definition which replaces the temporary stub one), the module starts to eat its own dogfood by using its own pattern matching.
That function, for instance, decides whether a pattern is "trivial" or not, using pattern matching itself on the pattern matching notation.
The string quasiliteral pattern's expansion relies heavily on pattern matching, also.
https://docs.racket-lang.org/reference/match.html