diff --git a/web/src/pages/docs/specs/physical-books.astro b/web/src/pages/docs/specs/physical-books.astro
index 67777d3..fd44eba 100644
--- a/web/src/pages/docs/specs/physical-books.astro
+++ b/web/src/pages/docs/specs/physical-books.astro
@@ -97,6 +97,22 @@ const examples = [
 					</section>
 
 					<section>
+						<h2
+							class="font-display font-bold text-xl text-surface-900 dark:text-white tracking-tight mb-3"
+						>
+							Conforms To
+						</h2>
+
+						<p class="mb-4">
+							For the spec below to apply the <kbd
+								class="rounded bg-surface-100 dark:bg-surface-700/60 px-1.5 py-0.5 font-mono text-[13px] text-surface-800 dark:text-surface-200"
+								>conformsTo</kbd
+							> value <em>must</em> be exactly <kbd
+								class="rounded bg-surface-100 dark:bg-surface-700/60 px-1.5 py-0.5 font-mono text-[13px] text-surface-800 dark:text-surface-200"
+								>{SPEC_URL}</kbd
+							>.
+						</p>
+
 						<h2
 							class="font-display font-bold text-xl text-surface-900 dark:text-white tracking-tight mb-3"
 						>