In IDL there is currently no way to enforce a relationship between two parameters like min/max.

It would be useful to be able to have a mechanism in IDL to enforce that a "min" param be less or equal to a "max" param, and that both cannot be set concurrently.

We had this issue with the replWriterThreadCount and replWriterMinThreadCount parameters, we want to enforce that replWriterThreadCount <= replWriterMinThreadCount, and that they cannot get updated concurrently as this could cause a crash (see: SERVER-115983). In order to achieve this we had to have a custom on_update and validator to take a lock during the update of the params. Having this capability in IDL would be easier, more standardized and less error-prone.