Specifying recursive modules?

["Jérémie Lumbroso" <jeremie.lumbroso@etu.upmc.fr>]

Hello,

I'd always thought of separating specification and definition as
simply not possible in OCaml, but OCaml's reference manual (3.10,
which is, as far as I can tell, the most recent version of the
documentation) seems to contradict my assumption:

http://caml.inria.fr/pub/docs/manual-ocaml/manual021.html#htoc100

It says that recursive specifications can be written as:

  <code>
  module rec <mod-name> : <mod-type> { and ... }
  </code>

What does this mean? When I attempt to use this feature in the
toplevel, it results in an error:

  <toplevel>
  # module rec Tmp : sig
      type t = Stop | Next of Tmp.t
    end**;;**
  Syntax error
  </toplevel>

On the off-chance that OCaml might explicitly need an "and", I also
tried adding a second dummy module to the definition, but no dice ...
When I try to use this feature in a .mli/.ml file coupling, I get the
same (syntax) error. Have I misunderstood the usage? Or has this been
removed since its introduction (and the documentation not updated
accordingly)? Or is this a bug?

Jérémie