code: function configureAria(element, scope){
        element.attr({
          id: attr.id || 'radio_' + $mdUtil.nextUid(),
          role: 'radio',
          'aria-checked': 'false'
        });
  
        $mdAria.expectWithText(element, 'aria-label');
      }
docs: Inject ARIA-specific attributes appropriate for each radio button