sub blah {
    return '}';
}

##</code><code>##

extract_bracketed($code, '{}') to handle this, but even that will still bomb on curlies in comments:
</p>
<code>
sub blah {
    # } is such a neat character
    return '}';
}

##</code><code>##

$code = blockize($code);

sub blockize {
    my ($code) = @_;
    
    # describe a block:
    use re 'eval';
    my $comment = qr/#[^\n]*/;
    my $single_quoted = qr/' [^\\']+ (?: \\. [^\\']+  )* '/;
    my $double_quoted = qr/" [^\\"]+ (?: \\. [^\\"]+  )* "/;
    my $block;
    $block = qr/
        { (?:
              (?> [^#'"{}]+ )
            | $comment
            | $single_quoted
            | $double_quoted
            | (??{$block})
        )* }
    /x;
    
    # now that we have a block definition set up, its just a simple substitution
    $code =~ s/sub \s+ (\w+) \s+ ($block)/ format_code("$1", "$2") /gex;
    return $code;
    
    sub format_code {
        my ($name, $block) = @_;
        $block =~ s/\n/\n    /g;
        return "{\n    sub $name $block\n}";
    }
}

##</code><code>##

sub blockize {
    my ($code) = @_;
    
    # describe a block:
    use re 'eval';
    use Regex::Common qw(delimited comment);
    my $block;
    $block = qr/
        { (?:
              (?> [^#'"{}]+ )
            | $RE{comment}{Perl}
            | $RE{delimited}{-delim=>"'"}
            | $RE{delimited}{-delim=>'"'}
            | (??{$block})
        )* }
    /x;
    
    # now that we have a block definition set up, its just a simple substitution
    $code =~ s/sub \s+ (\w+) \s+ ($block)/ format_code("$1", "$2") /gex;
    return $code;
    
    sub format_code {
        my ($name, $block) = @_;
        $block =~ s/\n/\n    /g;
        return "{\n    sub $name $block\n}";
    }
}