code: public RequestToken save(SaveMode mode,BaasACL acl, int flags, BaasHandler<BaasDocument> handler) {
          BaasBox box = BaasBox.getDefaultChecked();
          if (mode == null) throw new IllegalArgumentException("mode cannot be null");
          Save save = new Save(box, mode,acl, this, flags, handler);
          return box.submitAsync(save);
      }
docs: Asynchronously saves this document on the server, with initial {@link com.baasbox.android.BaasACL}.
  @param mode {@link com.baasbox.android.SaveMode}
  @param acl the initial acl settings
  @param flags {@link com.baasbox.android.RequestOptions}
  @param handler a callback to be invoked with the result of the request
  @return a {@link com.baasbox.android.RequestToken} to handle the request.