Incomplete types question

[NoUseForAName via Digitalmars-d-learn]

In C my favorite way of achieving encapsulation is to use 
incomplete types. The module header contains the definition of an 
incomplete type and the prototypes for the public functions which 
operate on it. I have read D has incomplete types too however D 
does not have headers and as a C guy I do not know how to 
implement this scheme without a .h/.c separation.

As I said, in C I put the incomplete declaration in the header 
while keeping the complete declaration private to the module. How 
do I do this in D? I mean type is complete within the module 
itself (and thus can be instantiated there) but incomplete for 
clients (i.e. other modules) i.e. instantiating or modifying data 
of that type directly is impossible.

P.S.: It seems D lingo for incomplete types is "opaque types".