docs: function StanzaFetcher(db, getInterchangeSession) {
    var self = this;
    self.db = db;
    self._closed = false;
    self.getInterchangeSession = getInterchangeSession;
    self._highWaterMarks = new Chain(self._fetchMostRecentStanzaSeq.bind(self));
    events.EventEmitter.call(this);
  }