Suggestion for conditional validation

I'm wondering how one would suggest altering the code concerning validations in such a way that a conditional validator can be incorporated that is dependent on other values.

For example given an object that has a start and end date parameter. I'd like to validate that the end date is higher or equal to the start date.

Currently all validation is on a individual field basis. Which works well for 95% of the use cases. I was personally thinking of adjusting the ValidationHandler

Ktor-OpenAPI-Generator/src/main/kotlin/com/papsign/ktor/openapigen/validation/ValidationHandler.kt

Line 239 in f7e7048

handled.forEach { (handler, field) ->

to create perhaps a wrapper around it that will be able to validate the properties once all others are done. Considering the ValidationHandler is recursive this is in theory already kind of the case. I've yet to found a way that I see fitting well.

What suggestions would you have?
Would you feel this being a worthy contribution to the library?

In priciple the use case would be to wrap that in a new class that represents a date range and validate that.
But if you believe you can make an ergonomic alternative i will gladly accept it.