Below is the API for the OCaml standard library. It's directly copied over from the OCaml Manual, formatted to the Reason syntax and styled accordingly. The API docs are work-in-progress; we'll be polishing these gradually!
If you're targeting JavaScript, the API docs for BuckleScript includes all of below, plus JS-specific APIs.
module type OrderedType = sig .. endSet.Make.type t 
val compare : t -> t -> int
f such that
          f e1 e2 is zero if the elements e1 and e2 are equal,
          f e1 e2 is strictly negative if e1 is smaller than e2,
          and f e1 e2 is strictly positive if e1 is greater than e2.
          Example: a suitable ordering function is the generic structural
          comparison function Pervasives.compare.