code: function() {
      for (var i = 0, len = this.events.length; i < len; i++) {
        if (this.events[i].streamRevision > this.lastRevision) {
          this.lastRevision = this.events[i].streamRevision;
        }
      }
  
      return this.lastRevision;
    }
docs: This helper function calculates and returns the current stream revision.
  @returns {Number} lastRevision