Regarding the `next/2` behaviour for `ets`, `dets` and `mnesia` for non existing keys and `ordered_set` tables

[Ciprian Dorin Craciun]

Looking at the `next/2` documentation for `ets`, it states that for
`ordered_set` the function always returns the next key larger than the
input, regardless if the input key exists or not.

So I was wondering if this property also translates to the equivalent
`next` function in `dets` and `mnesia` tables for `ordered_set` type?

In fact my question is more: the documentation doesn't specify
anything about this, but if the implementation works in a given way,
can I take that as a "soft promise of not changing that behaviour", or
should I assume that there is a high likelihood of this behaviour
changing in the next few releases.  (My assumption is that both `dets`
and `mnesia` are quite stable, therefore I'm not expecting major
changes in the near future.)

Thanks,
Ciprian.