'+' . sub { ... }
    '+' . \&subname
    '+' . [\&subname]
    '+' . [\&subname, @args]
    ['+' . \&subname]
    ['+' . \&subname, @args]
    '+' . $coderef
    '+' . [$coderef]
    '+' . [$coderef, @args]
    ['+' . $coderef]
    ['+' . $coderef, @args]