diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6e70ba4..42b0aa7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -50,6 +50,9 @@ jobs:
           pnpm build
           diff -r "$RUNNER_TEMP/schemas-before-docs" dist
 
+      - name: Check reference code samples
+        run: node tests/reference-code-samples.cjs
+
       - name: Dry run release
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
diff --git a/.shins/index.js b/.shins/index.js
index a5eb4fb..62a90de 100644
--- a/.shins/index.js
+++ b/.shins/index.js
@@ -213,7 +213,8 @@ function clean(s) {
     s = s.split('<=').join('$3$');
     let a = s.split('```');
     for (let i=0;i<a.length;i++) {
-        if (!a[i].startsWith('xml')) {
+        // sanitize-html treats `<?php ... >` as a tag and drops it.
+        if (!a[i].startsWith('xml') && !a[i].startsWith('php')) {
             a[i] = sanitizeHtml(a[i],sanitizeOptions);
         }
     }
diff --git a/tests/reference-code-samples.cjs b/tests/reference-code-samples.cjs
new file mode 100644
index 0000000..260a5af
--- /dev/null
+++ b/tests/reference-code-samples.cjs
@@ -0,0 +1,19 @@
+const assert = require('node:assert/strict');
+const fs = require('node:fs');
+const path = require('node:path');
+
+// Reads the reference produced by `pnpm build:docs`.
+const html = fs.readFileSync(path.resolve(__dirname, '..', 'build/docs/index.html'), 'utf8');
+
+const samples = (lang) => html.split('<h2 id="').slice(1).flatMap((section) => {
+  const id = section.slice(0, section.indexOf('"'));
+  const pattern = new RegExp(`<pre class="highlight tab tab-${lang}"><code>([\\s\\S]*?)</code></pre>`, 'g');
+  return [...section.matchAll(pattern)].map((match) => ({ id, code: match[1] }));
+});
+
+const php = samples('php');
+assert.ok(php.length > 0, 'no PHP samples in build/docs/index.html');
+const truncated = php.filter(({ code }) => !code.startsWith('<span class="hljs-meta">&lt;?php</span>'));
+assert.equal(truncated.length, 0,
+  `PHP samples missing their opening lines: ${truncated.map(({ id }) => id).join(', ')}`);
+console.log(`PHP samples: ${php.length} complete`);