perl6/doc/lib/X/Syntax/Signature/InvocantMarker

(title)  class X::Syntax::Signature::InvocantMarker

    class X::Syntax::Signature::InvocantMarker does X::Syntax { }

Syntax error when the invocant in a signature is anywhere else than after the first parameter. For example

    :($a, $b: $c)

dies with

    ===SORRY!===
    Can only use : as invocant marker in a signature after the first parameter