[keyframe-selectors.html]
  ['entry 10%' should be a valid keyframe selector]
    expected: FAIL

  ['exit 60%' should be a valid keyframe selector]
    expected: FAIL

  ['calc(10%)' should be a valid keyframe selector]
    expected: FAIL

  ['calc(10% * sibling-index())' should be a valid keyframe selector]
    expected: FAIL

  ['calc(10% * sign(1em - 1px))' should be a valid keyframe selector]
    expected: FAIL

  ['entry calc(10%)' should be a valid keyframe selector]
    expected: FAIL

  ['exit calc(60%)' should be a valid keyframe selector]
    expected: FAIL