function start_element($parser, $name, $attrs) {
        $this->tag_number++;
        $handler = 'discard_data';
        switch(strtoupper($name)) {
            case 'DIGESTVALUE':
                $handler = 'parse_digest';
                break;
            case 'SIGNATUREVALUE':
                $handler = 'parse_signature';
                break;
            case 'OBJECT':
                $handler = 'parse_object';
                break;
            case 'RETRIEVALMETHOD':
                $this->key_URI = $attrs['URI'];
                break;
            case 'TIMESTAMP':
                $handler = 'parse_timestamp';
                break;
            case 'WWWROOT':
                $handler = 'parse_wwwroot';
                break;
            case 'CIPHERVALUE':
                $this->cipher[$this->tag_number] = '';
                $handler = 'parse_cipher';
                break;
            case 'FAULT':
                $handler = 'parse_fault';
            default:
                break;
        }
        xml_set_character_data_handler($this->parser, $handler);
        return true;
    }