A hook that is called when a named method is called. For example, "before calling login(), call this modifier first. They come in different types like 'before', 'after', 'augment'. More than one can be applied to a single method.
before 'login' => sub { # do this before calling login()
my $self = shift;
my $pw = shift;
warn "Called login() with $pw\n";
};