Implements hook_preprocess_HOOK() for block.tpl.php.
function user_preprocess_block(&$variables) {
if ($variables['block']->module == 'user') {
switch ($variables['block']->delta) {
case 'login':
$variables['attributes']['role'] = 'form';
break;
case 'new':
$variables['attributes']['role'] = 'complementary';
break;
case 'online':
$variables['attributes']['role'] = 'complementary';
break;
}
}
}