[sibling-function-descriptors.tentative.html]
  [sibling-index() should not be allowed in @font-feature-values descriptors]
    expected: FAIL
    bug: https://bugzilla.mozilla.org/show_bug.cgi?id=2042037

  [sibling-count() should not be allowed in @font-feature-values descriptors]
    expected: FAIL
    bug: https://bugzilla.mozilla.org/show_bug.cgi?id=2042037