code: function (id) {
      var self = this;
      self._unpublishedBuffer.remove(id);
      // To keep the contract "buffer is never empty in STEADY phase unless the
      // everything matching fits into published" true, we poll everything as soon
      // as we see the buffer becoming empty.
      if (! self._unpublishedBuffer.size() && ! self._safeAppendToBuffer)
        self._needToPollQuery();
    }
docs: Is called either to remove the doc completely from matching set or to move it to the published set later.