Only Perl can parse Perl 6
The regexes in Perl 5 are well-integrated and oft-copied by other languages. With Perl 6, the game changes quite a bit: regexes are no longer funny pieces of interpolating strings; they're code, much like methods. Their expressive power has been extended to be able to easily define whole language grammars. A natural consequence of this is that Perl 6 itself is defined and parsed using a Perl 6 grammar, and is extensible/mutable at runtime like any such grammar. The expected bootstrapping and introspection hilarity follows from the circular nature of Perl 6 defining itself through its own constructs. If Perl 6 is to be changed through Perl 6, it more or less has to be defined in Perl 6.