fix(w3c/conformance): warn when conformance section is marked informative

src/w3c/conformance.js

@@ -79,9 +79,20 @@ function processConformance(conformance, conf) {
  * @param {Conf} conf
  */
 export function run(conf) {
+  /** @type {HTMLElement | null} */
   const conformance = document.querySelector("section#conformance");
-  if (conformance && !conformance.classList.contains("override")) {
-    processConformance(conformance, conf);
+  if (conformance) {
+    if (conformance.classList.contains("informative")) {
+      conformance.classList.remove("informative");
+      const msg =
+        "Conformance sections are normative by definition. The `informative` class has been removed.";
+      const hint =
+        'Remove `class="informative"` from `<section id="conformance">` to avoid this warning.';
+      showWarning(msg, name, { hint, elements: [conformance] });
+    }
+    if (!conformance.classList.contains("override")) {
+      processConformance(conformance, conf);
+    }
   }
   // Warn when there are RFC2119/RFC8174 keywords, but not conformance section
   if (!conformance && Object.keys(rfc2119Usage).length) {

tests/spec/w3c/conformance-spec.js

@@ -64,6 +64,32 @@ describe("W3C — Conformance", () => {
     expect(doc.querySelectorAll("#conformance .rfc2119")).toHaveSize(0);
   });
 
+  it("removes `informative` class and warns when conformance section is marked informative", async () => {
+    const body = `
+      <section id="conformance" class="informative">
+        <p>CONFORMANCE</p>
+      </section>
+      <section>
+        <h2>my section</h2>
+        <p>MUST be tested.</p>
+      </section>
+    `;
+    const doc = await makeRSDoc(makeStandardOps({}, body));
+    const conformance = doc.getElementById("conformance");
+    // The informative class should have been removed
+    expect(conformance.classList.contains("informative")).toBeFalse();
+    // A warning should be emitted, not an error
+    const warnings = doc.respec.warnings.filter(
+      w => w.plugin === "w3c/conformance"
+    );
+    expect(warnings).toHaveSize(1);
+    expect(warnings[0].message).toContain("normative");
+    expect(warnings[0].hint).toContain("informative");
+    expect(
+      doc.respec.errors.filter(e => e.plugin === "w3c/conformance")
+    ).toHaveSize(0);
+  });
+
   it("allows conformance section to be completely overridden via .override css class", async () => {
     const body = `
       <section>