Generates a comprehensive terms index — all terms defined in this spec and all terms referenced from other specs, in a single searchable section.

<section id="index" class="appendix">
  <!-- ReSpec generates the index here -->
</section>

<section id="index" class="appendix">
  <h2>Index of All Terms</h2>
  <p>Defined terms and external references used in this specification.</p>
  <!-- Index generated after custom content -->
</section>

<section id="index" class="appendix prefer-full-spec-title">
  <!-- Shows "DOM Standard" instead of "[DOM]" -->
</section>

• Shows both locally defined terms (<dfn>) and externally referenced terms (via xref)
• Clicking a term in the index jumps to its definition or first use in the document
• Adding class="prefer-full-spec-title" shows full spec titles (e.g., "DOM Standard") instead of shortnames (e.g., "[DOM]")
• Typically placed as an informative appendix