docs: function(other) {
        other.names.forEach(function(name) { this.names.add(name); }.bind(this));
  
        // Don't use pushEvent(), which would lose special start, end.
        this.associatedEvents.addEventSet(other.associatedEvents);
        this.start = Math.min(this.start, other.start);
        this.end = Math.max(this.end, other.end);
      }