Method move

/**
 * Method to move a row in the ordering sequence of a group of rows defined by an SQL WHERE clause.
 * Negative numbers move the row up in the sequence and positive numbers move it down.
 *
 * @param   integer  $delta  The direction and magnitude to move the row in the ordering sequence.
 * @param   string   $where  WHERE clause to use for limiting the selection of rows to compact the
 *                           ordering values.
 *
 * @return  mixed    Boolean true on success.
 *
 * @since   1.7.0
 */
public function move($delta, $where = '')
{
    $k = $this->_tbl_key;
    $pk = $this->{$k};
    $query = $this->_db->getQuery(true)->select($k)->from($this->_tbl)->where('parent_id = ' . $this->parent_id);
    if ($where) {
        $query->where($where);
    }
    if ($delta > 0) {
        $query->where('rgt > ' . $this->rgt)->order('rgt ASC');
        $position = 'after';
    } else {
        $query->where('lft < ' . $this->lft)->order('lft DESC');
        $position = 'before';
    }
    $this->_db->setQuery($query);
    $referenceId = $this->_db->loadResult();
    if ($referenceId) {
        return $this->moveByReference($referenceId, $position, $pk);
    } else {
        return false;
    }
}