code: function onWritten(writeErr) {
        var flags = fo.getFlags({
          overwrite: optResolver.resolve('overwrite', file),
          append: optResolver.resolve('append', file),
        });
        if (fo.isFatalOverwriteError(writeErr, flags)) {
          return callback(writeErr);
        }
  
        callback(null, file);
      }
docs: This is invoked by the various writeXxx modules when they've finished writing the contents.