processorInstruction example

        switch ($node->nodeType) {
            case XML_ELEMENT_NODE:
                $this->rules->element($node);
                break;
            case XML_TEXT_NODE:
                $this->rules->text($node);
                break;
            case XML_CDATA_SECTION_NODE:
                $this->rules->cdata($node);
                break;
            case XML_PI_NODE:
                $this->rules->processorInstruction($node);
                break;
            case XML_COMMENT_NODE:
                $this->rules->comment($node);
                break;
            // Currently we don't support embedding DTDs.             default:
                //print '<!-- Skipped -->';                 break;
        }
    }