// Headers out of order (i.e. h2 before h1, etc.)
h2 ~ h1,
h3 ~ h1,
h4 ~ h1,
h5 ~ h1,
h6 ~ h1,
h3 ~ h2:first-of-type,
h4 ~ h2:first-of-type,
h5 ~ h2:first-of-type,
h6 ~ h2:first-of-type,
h4 ~ h3:first-of-type,
h5 ~ h3:first-of-type,
h6 ~ h3:first-of-type,
h5 ~ h4:first-of-type,
h6 ~ h4:first-of-type,
h6 ~ h5:first-of-type {
  @include warning("Invalid order");
}