 the standard
       * static `observedAttributes` array.
       *
       * Attribute names are mapped to property names using the `dash-case` to
       * `camelCase` convention
       *
       */
      static createPropertiesForAttributes() {
        let a$ = this.observedAttributes;
        for (let i=0; i < a$.length; i++) {
          this.prototype._createPropertyAccessor(caseMap.dashToCamelCase(a$[i]));
        }
      }

      constructor() {
        super();
        this._initializeProperties();
    