private function _sanitize_class() {
		if ( isset( $this->attr['class'] ) && is_string( $this->attr['class'] ) ) {
			$this->attr['class'] = explode( ' ', $this->attr['class'] );
		}
		if ( !isset( $this->attr['class'] ) || !is_array( $this->attr['class'] ) ) {
			$this->attr['class'] = array();
		}
	}