       this.setAttribute("heading", value);
        }
        get visible() {
            return this.hasAttribute("visible");
        }
        set visible(value) {
            if (value) {
                this.setAttribute("visible", "");
            } else {
                this.removeAttribute("visible");
            }
        }
        static get observedAttributes() {
            return ["visible", "heading", "mode"];
        }
        attributeChangedCallback(name, oldValue, newValue) {
            i