Currently, when an invalid validation formula is used, the Spreadsheet throws a js exception.
For example: https://dojo.telerik.com/AWEyIHoW
Open the Data/Data Validation dialogue on cell A3 and modify the Value of the Formula into an Invalid formula (e.g. : “>3”)
A parse error is thrown.
It would be a nice improvement, if instead of throwing a js exception, the user is notified about the invalid formula through a dialog showing a relevant message.