<input name="test" type="text" value="test" required/>

function override_mce_options($initArray) {
$opts = '*[*]';
$initArray['valid_elements'] = $opts;
$initArray['extended_valid_elements'] = $opts;
return $initArray;

remove_filter('the_content', 'wpautop');

{selector:"input",attributes:["required"], split:false, expand:false, deep:true}