docs: function(event) {
        // Usually, this method will be called while iterating over a list of
        // events sorted by start time, so this method won't usually change
        // this.start. However, this will sometimes be called for ProtoIRs created
        // by previous handlers, in which case event.start could possibly be
        // before this.start.
        this.start = Math.min(this.start, event.start);
        this.end = Math.max(this.end, event.end);
        this.associatedEvents.push(event);
      }