speced · marcoscaceres · May 9, 2026 · May 13, 2026 · May 13, 2026 · May 13, 2026
diff --git a/src/core/link-to-dfn.js b/src/core/link-to-dfn.js
@@ -170,7 +170,8 @@ function collectDfns(title) {
       if ("idl" in dfn.dataset || dfnType !== "dfn") {
         result.get(dfnFor)?.set("idl", dfn);
       }
-      addId(dfn, "dfn", title);
+      const idText = dfnFor ? `${dfnFor}-${title}` : title;
+      addId(dfn, "dfn", idText);
     }
   }
 

diff --git a/src/core/location-hash.js b/src/core/location-hash.js
@@ -6,6 +6,7 @@
 // the window to the correct point in the document when processing is done.
 
 export const name = "core/location-hash";
+const DFN_ID_PREFIX = "dfn-";
 
 export function run() {
   if (!window.location.hash) {
@@ -39,6 +40,37 @@ export function run() {
       const updatedElement = document.getElementById(id);
       if (updatedElement) {
         newHash = id;
+      } else if (id.startsWith(DFN_ID_PREFIX)) {
+        const legacyTerm = id.slice(DFN_ID_PREFIX.length);
+        const numericSuffixMatch = legacyTerm.match(/^(.+)-(\d+)$/);
+        const termWithLeadingHyphen = `-${legacyTerm}`;
+        const scopedDfnElements = [
+          ...document.querySelectorAll(
+            `[data-dfn-type][id^='${DFN_ID_PREFIX}']`
+          ),
+        ];
+        let matchingElements = scopedDfnElements.filter(({ id }) => {
+          const scopedId = id.slice(DFN_ID_PREFIX.length);
+          return (
+            scopedId === legacyTerm || scopedId.endsWith(termWithLeadingHyphen)
+          );
+        });
+        if (!matchingElements.length && numericSuffixMatch) {
+          const [, baseTerm, index] = numericSuffixMatch;
+          const baseTermWithLeadingHyphen = `-${baseTerm}`;
+          matchingElements = scopedDfnElements.filter(({ id }) => {
+            const scopedId = id.slice(DFN_ID_PREFIX.length);
+            return (
+              scopedId === baseTerm ||
+              scopedId.endsWith(baseTermWithLeadingHyphen)
+            );
+          });
+          if (matchingElements[Number(index)]) {
+            newHash = matchingElements[Number(index)].id;
+          }
+        } else if (matchingElements.length === 1) {
+          newHash = matchingElements[0].id;
+        }
       }
     }
     window.location.hash = `#${newHash}`;

diff --git a/tests/spec/core/link-to-dfn-spec.js b/tests/spec/core/link-to-dfn-spec.js
@@ -17,11 +17,36 @@ describe("Core — Link to definitions", () => {
     const doc = await makeRSDoc(ops);
     const a = doc.getElementById("testAnchor");
     expect(a).toBeTruthy();
-    expect(a.hash).toBe("#dfn-test");
+    expect(a.hash).toBe("#dfn-window-test");
     const decodedHash = decodeURIComponent(a.hash);
     expect(doc.getElementById(decodedHash.slice(1))).toBeTruthy();
   });
 
+  it("uses data-dfn-for in generated IDs for duplicate terms", async () => {
+    const body = `
+      <section>
+        <h2>Test section</h2>
+        <p>
+          <dfn data-dfn-for="Request">state</dfn>
+          <dfn data-dfn-for="Response">state</dfn>
+          <a data-link-for="Request" data-link-type="dfn" id="requestState">state</a>
+          <a data-link-for="Response" data-link-type="dfn" id="responseState">state</a>
+        </p>
+      </section>`;
+    const ops = makeStandardOps(null, body);
+    const doc = await makeRSDoc(ops);
+    const [requestState, responseState] = doc.querySelectorAll("dfn");
+    expect(requestState.id).toBe("dfn-request-state");
+    expect(responseState.id).toBe("dfn-response-state");
+    expect(requestState.id).not.toMatch(/-\d+$/);
+    expect(responseState.id).not.toMatch(/-\d+$/);
+
+    const requestStateLink = doc.getElementById("requestState");
+    const responseStateLink = doc.getElementById("responseState");
+    expect(requestStateLink.hash).toBe("#dfn-request-state");
+    expect(responseStateLink.hash).toBe("#dfn-response-state");
+  });
+
   it("links to IDL definitions and wraps in code if needed", async () => {
     const bodyText = `
       <section data-link-for="Request">

diff --git a/tests/spec/core/location-hash-legacy-indexed.html b/tests/spec/core/location-hash-legacy-indexed.html
@@ -0,0 +1,25 @@
+<!doctype html>
+<html>
+  <meta charset="utf-8" />
+  <title>Legacy Indexed Hashes</title>
+  <script class="remove">
+    var respecConfig = {
+      specStatus: "ED",
+      shortName: "basics",
+      editors: [{ name: "Robin Berjon", url: "http://berjon.com/" }],
+      github: "speced/respec",
+      group: "webapps",
+    };
+  </script>
+  <section id="abstract">
+    <p>Basic doc</p>
+  </section>
+  <section id="sotd">
+    <p>CUSTOM PARAGRAPH</p>
+  </section>
+  <section>
+    <h2>Legacy indexed terms</h2>
+    <p><dfn data-dfn-for="Window">unsafe current time</dfn></p>
+    <p><dfn data-dfn-for="Worker">unsafe current time</dfn></p>
+  </section>
+</html>
diff --git a/tests/spec/core/location-hash-spec.js b/tests/spec/core/location-hash-spec.js
@@ -6,6 +6,7 @@ describe("Core — Location Hash", () => {
   afterAll(flushIframes);
   const ops = makeStandardOps();
   const simpleURL = "/tests/spec/core/simple.html";
+  const legacyIndexedURL = "/tests/spec/core/location-hash-legacy-indexed.html";
 
   describe("legacy fragment format", () => {
     it("leaves editor defined id alone, even if they include illegal chars", async () => {
@@ -22,7 +23,12 @@ describe("Core — Location Hash", () => {
     it("recovers legacy encoded hashes for slots", async () => {
       const testURL = `${simpleURL}#dfn-%5B%5Bescapedslot%5D%5D`;
       const doc = await makeRSDoc(ops, testURL);
-      expect(doc.location.hash).toBe("#dfn-escapedslot");
+      expect(doc.location.hash).toBe("#dfn-test-escapedslot");
+    }, 20000);
+    it("recovers legacy numeric-suffixed hashes", async () => {
+      const testURL = `${legacyIndexedURL}#dfn-unsafe-current-time-0`;
+      const doc = await makeRSDoc(ops, testURL);
+      expect(doc.location.hash).toBe("#dfn-window-unsafe-current-time");
     }, 20000);
   });
 });
diff --git a/tests/spec/core/xref-spec.js b/tests/spec/core/xref-spec.js
@@ -852,7 +852,7 @@ describe("Core — xref", () => {
 
       // as base == [[type]], it is treated as a local internal slot
       const link1 = doc.querySelector("#link1 a");
-      expect(link1.getAttribute("href")).toBe("#dfn-type");
+      expect(link1.getAttribute("href")).toBe("#dfn-window-type");
       expect(link1.firstElementChild.localName).toBe("code");
 
       // the base "Credential" is used as "forContext" for [[type]]