public function shiftColumn($fromColumn=NULL,$toColumn=NULL) {
		$fromColumn = strtoupper($fromColumn);
		$toColumn = strtoupper($toColumn);

		if (($fromColumn !== NULL) && (isset($this->_columns[$fromColumn])) && ($toColumn !== NULL)) {
			$this->_columns[$fromColumn]->setParent();
			$this->_columns[$fromColumn]->setColumnIndex($toColumn);
			$this->_columns[$toColumn] = $this->_columns[$fromColumn];
			$this->_columns[$toColumn]->setParent($this);
			unset($this->_columns[$fromColumn]);

			ksort($this->_columns);
		}

		return $this;
	}