this.expanded_=true;this.arrowVisible_=false;this.selectionGenerator_=undefined;this.updateContents_();},get heading(){return this.heading_;},set heading(text){if(this.heading_===text)return;this.heading_=text;this.updateContents_();},set arrowVisible(val){if(this.arrowVisible_===val)return;this.arrowVisible_=!!val;this.updateContents_();},set tooltip(text){this.$.heading.title=text;},set selectionGenerator(generator){if(this.selectionGenerator_===generator)return;this.selectionGenerator_=genera...