[hobnail]

That "only defined once" rule seems bad to me. What I have in my standard stylesheet is like the following. All the common shared stuff in one rule and then the size stuff in separate rules. Following their rule would make maintenance a hassle since you'd have to duplicate stuff using copy and paste. As a programmer I learned that copy and paste was a bad "code smell".

h1, h2, h3, h4 {
    break-inside: avoid;
    break-after: avoid;
    font-weight: bold;
    hyphens: none;
    margin-bottom: 0em;
    margin-top: 1em;
    page-break-after: avoid;
    page-break-inside: avoid;
    text-align: center;
    text-indent: 0em;
}

h1 {
    font-size: 1.44em;
}

h2 {
    font-size: 1.3em;
}

h3 {
    font-size: 1.12em;
}

h4 {
    font-size: 1em;
}