[background-position-x-valid.html]
  [e.style['background-position-x'\] = "x-end" should set the property value]
    expected: FAIL

  [e.style['background-position-x'\] = "0.5em, x-start, x-end" should set the property value]
    expected: FAIL

  [e.style['background-position-x'\] = "x-start" should set the property value]
    expected: FAIL