How does a collection satisfy a minElement() requirement in the general case? Making the predicate version required would let the no-argument version be provided as an extension for comparable elements that simply calls the required method with <.

> How does a collection satisfy a minElement() requirement in the general case?

With a default implementation that compares elements one by one.

> Making the predicate version required

That version would be a pure extension, and wouldn't allow customization, since no customization can be faster than the default.

I guess I'm asking what an Array<UIImage> would return for this? Would it simply be undefined for sequences of elements that aren't Comparable, like `first` for unordered collections?

Right, the no-arg method will only be defined for collections of comparable elements.

I'm not super happy with us continuing to add customization points willy-nilly. These have a definite code size cost, and we should start taking that into account or come up with an alternate implementation.