text: class Fragment extends Base {
  
    constructor(brush) {
      super();
      this.id = Misc.guid;
      this.brush = brush;
      this.selection = null;
      this.domain = null;
      this.range = null;
      this.panelWidth = null;
    }
  
    get toString() {
      return `fragment: ${this.id}, 
        selection: [${this.selection.join(',')}], 
        domain: [${this.domain.join(',')}]
        range: [${this.range && this.range.join(',')}]
        panelWidth: ${this.panelWidth}`;
    }
  }