<!DOCTYPE html> <!-- fieldset with one valid element and you dynamically add a barred constraint validation element --> <html> <head> <style> fieldset:valid { display:none } </style> <script> function onLoadHandler() { document.getElementById("fieldset").appendChild(document.getElementById('i')); document.documentElement.className=''; } </script> </head> <body onload='onLoadHandler();'> <input id='i' value='foo' readonly> <fieldset id="fieldset" id="fieldset"> <input id='j' value='bar' required> </fieldset> </body> </html>