perl6/doc/lib/X/Syntax/P5

(title)  class X::Syntax::P5

    class X::Syntax::P5 does X::Syntax { }

Syntax error thrown when some piece of code is clearly Perl 5, not Perl 6. For example

    for my $a (1, 2) { }

dies with

    ===SORRY!===
    This appears to be Perl 5 code