StopThis test cases exercises stop comments.
The next value is bar, and it should be missing from
     the documentation. There is also an entire module, M
    , which should also be hidden. It contains a nested stop comment,
     but that stop comment should not turn documentation back on in this
     outer module, because stop comments respect scope.
   
Documentation is on again.
Now, we have a nested module, and it has a stop comment between its two items. We want to see that the first item is displayed, but the second is missing, and the stop comment disables documenation only in that module, and not in this outer module.
      module N
      
       : sig ... 
       end
      
     
    The first comment can also be a stop-comment. The test case 
    stop_first_comment.mli is testing the same thing but
     at the toplevel. We should see bar inside 
    O.
   
      module O
      
       : sig ... 
       end
      
     
    The top-comment computation must not mess with stop comments.
      module P
      
       : sig ... 
       end
      
     
    Doc.