public function push($type, $value, $reference = NULL) {
		$this->_stack[$this->_count++] = array('type'		=> $type,
											   'value'		=> $value,
											   'reference'	=> $reference
											  );
		if ($type == 'Function') {
			$localeFunction = PHPExcel_Calculation::_localeFunc($value);
			if ($localeFunction != $value) {
				$this->_stack[($this->_count - 1)]['localeValue'] = $localeFunction;
			}
		}
	}