How to use the nested module in OCaml object files

Hi all,

I'm writing a Coq plugin and I need some functions in Coq source. For
example,

module Named :sig
   module Declaration :
   sig
      type t = LocalAssum of Id.t * Constr.t
             | LocalDef of Id.t * Constr.t * Constr.t
      ...
   end
   ...end

This module is in kernel/context.ml. I want use the constructor LocalAssum
and LocalDef to parse something, but I can't use them. It seems that the
.cmi and .cma file in $COQLIB only expose the members in context.ml but not
the ones in nested modules. I've tried adding open
Context.Named.Declaration but
compiler told me "Error: Unbound module Context.Named".

Any help appreciated.

Thanks, Hengruo