Add an option to select max 1 or n options.

[leroy0211]

It would be great to add an option to select a maximum of 1 or n options.

My use case is to display a list of options, where a person can only select 1 option. But if he is wrong he must have the ability to uncheck that option. That's the reason I cannot use radio's, but I have to use checkboxes.

Se let's extend my use case so a user can only select a maximum of n options.