[required-optional.html]
  [':required' matches required <input>s, <select>s and <textarea>s]
    expected: FAIL

  [':optional' matches elements <input>s, <select>s and <textarea>s that are not required]
    expected: FAIL

  [':required' doesn't match elements whose required attribute has been removed]
    expected: FAIL

  [':optional' matches elements whose required attribute has been removed]
    expected: FAIL

  [':required' matches elements whose required attribute has been added]
    expected: FAIL

  [':optional' doesn't match elements whose required attribute has been added]
    expected: FAIL