constructor(customLoader, customTooltip) {
      this._active = null;
      this._handlers = {};
      this._loader = customLoader || loader();
      this._tooltip = customTooltip || defaultTooltip$1;
    }
Create a new Handler instance.
@param {object} [customLoader] - Optional loader instance for
  href URL sanitization. If not specified, a standard loader
  instance will be generated.
@param {function} [customTooltip] - Optional tooltip handler
  function for custom tooltip display.
@constructor