No, you're right. What's in the top-level curlies ends up being top-level code in the package. My parsers always look like:

use strict;
use warnings;

my $grammar = <<'__EOI__';

    {
        use strict;
        use warnings;
    }

    ...

__EOI__
[download]

Note the use of heredocs. Much better than q{} since you don't have to escape some backslashes and some curlies. For example, to have a production match a single backslash,

Single quote heredoc: rule: /\\/
Single quote literal: rule: /\\\/ or rule: /\\\\/