| PASS ':required' matches required <input>s, <select>s and <textarea>s | |
| PASS ':optional' matches elements <input>s, <select>s and <textarea>s that are not required | |
| PASS ':required' doesn't match elements whose required attribute has been removed | |
| PASS ':optional' matches elements whose required attribute has been removed | |
| PASS ':required' matches elements whose required attribute has been added | |
| PASS ':optional' doesn't match elements whose required attribute has been added | |