protected function pCommaSeparated(array $nodes, $max_len = 80)
    {
        $result = '';
        $line = '';
        $strings = $this->pIterator($nodes);
        foreach ($strings as $node_str) {
            if ($line !== '' && strlen($line) + strlen($node_str) > $max_len) {
                $result .= $line . ",\n";
                $line = '    ' . $node_str;
            } else {
                $line .= ($line !== '' ? ', ' : '') . $node_str;
            }
        }
        $result .= $line;
        return $result;
    }