code: function( options ){
        this.options = options;
  
        registrant.call( this, options );
  
        // make sure layout has _private for use w/ std apis like .on()
        if( !is.plainObject( this._private ) ){
          this._private = {};
        }
  
        this._private.cy = options.cy;
        this._private.listeners = [];
  
        this.createEmitter();
      }
docs: fill in missing layout functions in the prototype