code: function compile (tElement, tAttrs) {
      var wrapper = angular.element(tElement[0].getElementsByClassName('md-slider-wrapper'));
  
      var tabIndex = tAttrs.tabindex || 0;
      wrapper.attr('tabindex', tabIndex);
  
      if (tAttrs.disabled || tAttrs.ngDisabled) wrapper.attr('tabindex', -1);
  
      tElement.attr('role', 'slider');
  
      $mdAria.expect(tElement, 'aria-label');
  
      return postLink;
    }
docs: ********************************************************** Private Methods **********************************************************