Rakudo grammar versus STD.pm
Q: Why doesn't Rakudo just use STD.pm directly?
A1: STD.pm requires some features we don't have implemented yet
A2: STD.pm continues to evolve -- changes to STD.pm sometimes imply major Rakudo refactors
Rakudo's grammar follows STD.pm as closely as we can
Periodically we "re-sync" Rakudo's grammar with latest STD.pm refactors