Marks a section as an appendix. Appendix sections are lettered rather than numbered (A, B, C…). All sections following an appendix are also treated as appendices.

<section class="appendix">
  <h2>Acknowledgements</h2>
  <p>The editors thank the following for their contributions…</p>
</section>

• Being an appendix does not make a section informative — combine with class="informative" if needed
• Every section after the first appendix becomes an appendix — put appendices at the end of the document
• Appendix IDs and the ToC show letter labels (A, B, C…) instead of numbers