anchor.diff:      // Doc exists if CouchDB didn't throw an error status code
       >> asyncMap (function | Choice1Of2 _ -> true | Choice2Of2 _ -> false) 
   
  -let existsByExpression () = failwith "Not implemented"
  -
  -let existsByObject () = failwith "Not implemneted"
  -
  -let existsBySelector () = failwith "Not implemented"
  -
   let copy oldId newId props = 
       request oldId props
       |> headers (Map.ofSeq ["Destination", newId])
  
positive.code:     return docs
  }
  
  /// Retrieves a count of all documents matching the given selector.
  let countBySelector = convertMapToDict >> countByDictionary
  
  /// Checks that a document matching the given selector exists.
  let existsBySelector = convertMapToDict >> existsByDictionary
  
  let bulkInsert () = failwith "Not implemented"
  
  
negative.code:     allDocsRaw includeDocs options props 
      |> asyncMap (stringToDocumentList props.converter)
  
  let create document props = 
      request "" props
      |> body document
  