Open Objects example lacks explanation

[lxsmnsyc]

For example, in the Open Objects example

type tesla('a) = {
  ..
  drive: int => int
} as 'a;

The tutorial does not explain:

• What the alias does or does it affect all generics with the same keyword as the alias.
• How to implement an open object generics
• How to implement an open object interface

It also needs an example where an open object accepts another open object as a parameter, similar to this:

type a('a) = {
  ..
  myAMethod: unit => unit
} as 'a;

type b('b, 'a) = {
  ..
  /* some implementation that uses the generic */
} as 'a

I found this a problem when I was writing Reaxon, specially with this kind of types:

type subscription = Cancellable.Boolean.i;

type observer('observer, 'a) = {
  ..
  onSubscribe: subscription => unit,
  onSuccess: 'a => unit,
  onError: exn => unit,
} as 'observer;


type t('observer,'a) = {
  .
  subscribeWith: observer('observer, 'a) => unit,
};