public function setVar($varName, $varValue, $force = false)
    {
        if (isset($this->variableList[$varName]) && $force === false) {
            trigger_error('Variable "' . $varName . '" is already defined in Layout.', E_USER_WARNING);
            return false;
        }
        $this->variableList[$varName] = $varValue;
        return true;
    }