diff --git a/accelerometer/idlharness.https.html b/accelerometer/idlharness.https.html
index 3c3c96e88e8740..1f32be986855b7 100644
--- a/accelerometer/idlharness.https.html
+++ b/accelerometer/idlharness.https.html
@@ -15,7 +15,7 @@
   const idl_array = new IdlArray();
   idl_array.add_untested_idls(dom);
   idl_array.add_untested_idls('interface EventHandler {};');
-  idl_array.add_idls(generic_sensor, { only: ['Sensor'] });
+  idl_array.add_idls(generic_sensor, { only: ['Sensor', 'SensorOptions'] });
   idl_array.add_idls(accelerometer);
   idl_array.add_objects({
     Accelerometer: ['new Accelerometer();'],
diff --git a/background-fetch/interfaces.html b/background-fetch/interfaces.html
index f512e454071250..51e320e64379f0 100644
--- a/background-fetch/interfaces.html
+++ b/background-fetch/interfaces.html
@@ -12,15 +12,17 @@ <h1>idlharness test</h1>
 <script>
 'use strict';
 
-promise_test(function() {
-  return fetch('/interfaces/background-fetch.idl')
-    .then(response => response.text())
-    .then(idls => {
-      var idlArray = new IdlArray();
-      idlArray.add_untested_idls('interface ServiceWorkerRegistration {};');
-      idlArray.add_untested_idls('[Exposed=ServiceWorker] interface ServiceWorkerGlobalScope {};');
-      idlArray.add_idls(idls);
-      idlArray.test();
-    });
+promise_test(async function () {
+  const idls = await fetch('/interfaces/background-fetch.idl').then(r => r.text());
+  const dom = await fetch('/interfaces/dom.idl').then(r => r.text());
+
+  var idlArray = new IdlArray();
+  idlArray.add_untested_idls('interface ServiceWorkerRegistration {};');
+  idlArray.add_untested_idls('[Exposed=ServiceWorker] interface ServiceWorkerGlobalScope {};');
+  idlArray.add_untested_idls('interface ExtendableEvent{};');
+  idlArray.add_untested_idls('dictionary ExtendableEventInit{};');
+  idlArray.add_untested_idls(dom, { only: ['EventTarget'] });
+  idlArray.add_idls(idls);
+  idlArray.test();
 }, 'Exposed interfaces in a Document.');
 </script>
diff --git a/background-fetch/interfaces.worker.js b/background-fetch/interfaces.worker.js
index 89a7cb3da0ad73..9b8d0264a56f99 100644
--- a/background-fetch/interfaces.worker.js
+++ b/background-fetch/interfaces.worker.js
@@ -3,16 +3,18 @@
 importScripts('/resources/testharness.js');
 importScripts('/resources/WebIDLParser.js', '/resources/idlharness.js');
 
-promise_test(function() {
-  return fetch('/interfaces/background-fetch.idl')
-    .then(response => response.text())
-    .then(idls => {
-      var idlArray = new IdlArray();
-      idlArray.add_untested_idls('interface ServiceWorkerRegistration {};');
-      idlArray.add_untested_idls('[Exposed=ServiceWorker] interface ServiceWorkerGlobalScope {};');
-      idlArray.add_idls(idls);
-      idlArray.test();
-    });
+promise_test(async function() {
+  const idls = await fetch('/interfaces/background-fetch.idl').then(r => r.text());
+  const dom = await fetch('/interfaces/dom.idl').then(r => r.text());
+
+  var idlArray = new IdlArray();
+  idlArray.add_untested_idls('interface ServiceWorkerRegistration {};');
+  idlArray.add_untested_idls('[Exposed=ServiceWorker] interface ServiceWorkerGlobalScope {};');
+  idlArray.add_untested_idls('interface ExtendableEvent{};');
+  idlArray.add_untested_idls('dictionary ExtendableEventInit{};');
+  idlArray.add_untested_idls(dom, { only: ['EventTarget'] });
+  idlArray.add_idls(idls);
+  idlArray.test();
 }, 'Exposed interfaces in a Service Worker.');
 
 done();
diff --git a/clipboard-apis/async-interfaces.https.html b/clipboard-apis/async-interfaces.https.html
index d69fb70a731dfd..1f523e5d565dec 100644
--- a/clipboard-apis/async-interfaces.https.html
+++ b/clipboard-apis/async-interfaces.https.html
@@ -9,13 +9,13 @@
 <script>
 'use strict';
 
-function doTest(idls) {
+function doTest(idl, dom) {
   var idl_array = new IdlArray();
   idl_array.add_untested_idls('interface Navigator {};');
   idl_array.add_untested_idls('interface EventTarget {};');
-  for (let idl of idls) {
-    idl_array.add_idls(idl);
-  }
+  idl_array.add_untested_idls('dictionary PermissionDescriptor {};');
+  idl_array.add_untested_idls(dom, { only: ['Event', 'EventInit'] });
+  idl_array.add_idls(idl);
   idl_array.add_objects({
     Navigator: ['navigator'],
     Clipboard: ['navigator.clipboard'],
@@ -29,7 +29,11 @@
 }
 
 promise_test(() => {
-  return Promise.all(["/interfaces/clipboard-apis.idl"].map(fetchText))
-    .then(doTest);
+  return Promise.all(
+    [
+      "/interfaces/clipboard-apis.idl",
+      "/interfaces/dom.idl",
+    ].map(fetchText))
+    .then(([idl, dom]) => doTest(idl, dom));
 }, "Test driver");
 </script>
diff --git a/content-security-policy/securitypolicyviolation/idl.html b/content-security-policy/securitypolicyviolation/idl.html
index a4f9e68f8314db..2853b868e57a4b 100644
--- a/content-security-policy/securitypolicyviolation/idl.html
+++ b/content-security-policy/securitypolicyviolation/idl.html
@@ -21,9 +21,6 @@
       long           lineNumber;
       long           columnNumber;
   };
-
-  interface Event {
-  };
 </script>
 <script type="text/plain" id="tested">
   [Constructor(DOMString type, optional SecurityPolicyViolationEventInit eventInitDict)]
@@ -42,11 +39,16 @@
   };
 </script>
 <script>
+  promise_test(async function() {
+    let dom = await fetch('/interfaces/dom.idl').then(r => r.text());
+
     var idl_array = new IdlArray();
     idl_array.add_untested_idls(document.querySelector('#untested').textContent);
+    idl_array.add_untested_idls(dom, { only: ['Event', 'EventInit'] });
     idl_array.add_idls(document.querySelector('#tested').textContent);
     idl_array.add_objects({
-      SecurityPolicyViolationEvent: ['new SecurityPolicyViolationEvent({})']      
+      SecurityPolicyViolationEvent: ['new SecurityPolicyViolationEvent({})']
     });
     idl_array.test();
+  })
 </script>
diff --git a/cookie-store/idlharness.tentative.html b/cookie-store/idlharness.tentative.html
index e9ffab3730f3b5..e313b04ff8f3ab 100644
--- a/cookie-store/idlharness.tentative.html
+++ b/cookie-store/idlharness.tentative.html
@@ -10,21 +10,38 @@
 'use strict';
 
 promise_test(async t => {
-  const urls = ['/interfaces/html.idl', '/interfaces/cookie-store.idl'];
-  const [html, cookie_store] = await Promise.all(
-    urls.map(url => fetch(url).then(response => response.text())));
+  const urls = [
+    '/interfaces/uievents.idl',
+    '/interfaces/dom.idl',
+    '/interfaces/html.idl',
+    '/interfaces/cookie-store.idl'
+  ];
+  const [uievents, dom, html, cookie_store] = await Promise.all(
+    urls.map(url => fetch(url).then(r => r.text())));
 
   const idl_array = new IdlArray();
 
   // Dependencies of HTML
+  idl_array.add_untested_idls(dom, { only: [
+    'Event',
+    'EventInit',
+    'EventTarget',
+    'HTMLCollection',
+    'NodeList',
+  ] });
   idl_array.add_untested_idls('interface Document {};');
+  idl_array.add_untested_idls('interface Element {};');
   idl_array.add_untested_idls('interface LinkStyle {};');
   idl_array.add_untested_idls('interface SVGElement {};');
   idl_array.add_untested_idls(html);
+  idl_array.add_untested_idls(uievents, { only: [
+    'UIEvent',
+    'UIEventInit',
+    'MouseEvent',
+    'MouseEventInit',
+    'EventModifierInit',
+  ] });
 
-  idl_array.add_untested_idls('interface Event {};');
-  idl_array.add_untested_idls('dictionary EventInit {};');
-  idl_array.add_untested_idls('interface EventTarget {};');
   idl_array.add_untested_idls(
     `[Global=ServiceWorker, Exposed=ServiceWorker]
      interface ServiceWorkerGlobalScope {};`);
diff --git a/css/cssom-view/interfaces.html b/css/cssom-view/interfaces.html
index c6e3662334e780..308c1b4e2647c6 100644
--- a/css/cssom-view/interfaces.html
+++ b/css/cssom-view/interfaces.html
@@ -17,11 +17,12 @@ <h1>CSSOM View IDL tests</h1>
 <script>
 "use strict";
 
-function doTest([html, dom, cssom, geometry, cssom_view]) {
+function doTest([html, dom, uievents, cssom, geometry, cssom_view]) {
 
   var idlArray = new IdlArray();
   var svg = "interface SVGElement : Element {};";
   idlArray.add_untested_idls(html + dom + svg + cssom + geometry);
+  idlArray.add_untested_idls(uievents, { only: ['UIEvent', 'UIEventInit', 'MouseEvent', 'MouseEventInit', 'EventModifierInit'] });
   idlArray.add_idls(cssom_view);
 
   idlArray.add_objects({
@@ -57,6 +58,7 @@ <h1>CSSOM View IDL tests</h1>
   // Have to wait for onload
   return Promise.all([fetchData("/interfaces/html.idl"),
                       fetchData("/interfaces/dom.idl"),
+                      fetchData("/interfaces/uievents.idl"),
                       fetchData("/interfaces/cssom.idl"),
                       fetchData("/interfaces/geometry.idl"),
                       fetchData("/interfaces/cssom-view.idl"),
diff --git a/css/cssom/interfaces.html b/css/cssom/interfaces.html
index e289c5a3496e24..b92da9fa18c4fb 100644
--- a/css/cssom/interfaces.html
+++ b/css/cssom/interfaces.html
@@ -31,7 +31,7 @@ <h1>CSSOM IDL tests</h1>
 "use strict";
 var style_element, svg_element, xmlss_pi;
 
-function doTest([html, dom, cssom]) {
+function doTest([html, dom, uievents, cssom]) {
   style_element = document.getElementById('styleElement');
   svg_element = document.getElementById('svgElement');
   xmlss_pi = document.getElementById('xmlssPiIframe').contentDocument.firstChild;
@@ -39,6 +39,7 @@ <h1>CSSOM IDL tests</h1>
   var idlArray = new IdlArray();
   var svg = "interface SVGElement : Element {};";
   idlArray.add_untested_idls(html + dom + svg);
+  idlArray.add_untested_idls(uievents, { only: ['UIEvent', 'UIEventInit', 'MouseEvent', 'MouseEventInit', 'EventModifierInit']});
   idlArray.add_idls(cssom);
 
   idlArray.add_objects({
@@ -81,6 +82,7 @@ <h1>CSSOM IDL tests</h1>
   // Have to wait for onload
   return Promise.all([fetchData("/interfaces/html.idl"),
                       fetchData("/interfaces/dom.idl"),
+                      fetchData("/interfaces/uievents.idl"),
                       fetchData("/interfaces/cssom.idl"),
                       waitForLoad()])
                 .then(doTest);
diff --git a/encrypted-media/idlharness.https.html b/encrypted-media/idlharness.https.html
index cd87ecdca26bd1..a609f9483e66b9 100644
--- a/encrypted-media/idlharness.https.html
+++ b/encrypted-media/idlharness.https.html
@@ -33,6 +33,7 @@ <h1 class="instructions">Description</h1>
                 idl_array.add_untested_idls("interface Navigator {};");
                 idl_array.add_untested_idls("interface HTMLMediaElement {};");
                 idl_array.add_untested_idls("interface Event {};");
+                idl_array.add_untested_idls("dictionary EventInit {};");
                 idl_array.add_untested_idls("interface EventTarget {};");
 
                 idl_array.add_idls(idls);
diff --git a/gamepad/idlharness.html b/gamepad/idlharness.html
index 833449d72b6faa..9719d02019602d 100644
--- a/gamepad/idlharness.html
+++ b/gamepad/idlharness.html
@@ -14,8 +14,9 @@
 promise_test(async () => {
   const idl_array = new IdlArray();
   const gamepad_idl = await fetch("/interfaces/gamepad.idl").then(r => r.text());
+  const dom = await fetch("/interfaces/dom.idl").then(r => r.text());
 
-  idl_array.add_untested_idls('interface Event {};');
+  idl_array.add_untested_idls(dom, {only: ['Event', 'EventInit']});
   idl_array.add_untested_idls('interface Navigator {};');
   idl_array.add_idls(gamepad_idl);
 
diff --git a/geolocation-sensor/idlharness.https.html b/geolocation-sensor/idlharness.https.html
index d674a79fa5faac..75d29ebaa80559 100644
--- a/geolocation-sensor/idlharness.https.html
+++ b/geolocation-sensor/idlharness.https.html
@@ -14,7 +14,7 @@
   const idl_array = new IdlArray();
   idl_array.add_untested_idls('interface EventTarget {};');
   idl_array.add_untested_idls('interface EventHandler {};');
-  idl_array.add_idls(generic_sensor, { only: ['Sensor'] });
+  idl_array.add_idls(generic_sensor, { only: ['Sensor', 'SensorOptions'] });
   idl_array.add_idls(geolocation_sensor);
   idl_array.add_objects({
     GeolocationSensor: ['new GeolocationSensor'],
diff --git a/gyroscope/idlharness.https.html b/gyroscope/idlharness.https.html
index ca552a98211262..4b3ed48a073aa0 100644
--- a/gyroscope/idlharness.https.html
+++ b/gyroscope/idlharness.https.html
@@ -15,7 +15,7 @@
   const idl_array = new IdlArray();
   idl_array.add_untested_idls(dom);
   idl_array.add_untested_idls('interface EventHandler {};');
-  idl_array.add_idls(generic_sensor, { only: ['Sensor'] });
+  idl_array.add_idls(generic_sensor, { only: ['Sensor', 'SensorOptions'] });
   idl_array.add_idls(gyroscope);
   idl_array.add_objects({
     Gyroscope: ['new Gyroscope();']
diff --git a/hr-time/idlharness.html b/hr-time/idlharness.html
index 4abaf6033fd437..d28cee3a70014b 100644
--- a/hr-time/idlharness.html
+++ b/hr-time/idlharness.html
@@ -16,8 +16,9 @@ <h1>High Resolution Time IDL tests</h1>
 <script>
 'use strict';
 
-function doTest([html, hr_time]) {
+function doTest([dom, html, hr_time]) {
   var idl_array = new IdlArray();
+  idl_array.add_untested_idls(dom, { only: ['EventTarget'] });
   idl_array.add_untested_idls(html, { only: ['WindowOrWorkerGlobalScope'] });
   idl_array.add_idls(hr_time);
   idl_array.add_objects({
@@ -32,7 +33,8 @@ <h1>High Resolution Time IDL tests</h1>
 }
 
 promise_test(() => {
-  return Promise.all(['/interfaces/html.idl',
+  return Promise.all(['/interfaces/dom.idl',
+                      '/interfaces/html.idl',
                       '/interfaces/hr-time.idl'].map(fetchText))
                 .then(doTest);
 }, 'Test driver');
diff --git a/magnetometer/idlharness.https.html b/magnetometer/idlharness.https.html
index 3ab2bc279ba59e..904869ebd6dbf6 100644
--- a/magnetometer/idlharness.https.html
+++ b/magnetometer/idlharness.https.html
@@ -15,7 +15,7 @@
   const idl_array = new IdlArray();
   idl_array.add_untested_idls(dom);
   idl_array.add_untested_idls('interface EventHandler {};');
-  idl_array.add_idls(generic_sensor, { only: ['Sensor'] });
+  idl_array.add_idls(generic_sensor, { only: ['Sensor', 'SensorOptions'] });
   idl_array.add_idls(magnetometer);
   idl_array.add_objects({
     Magnetometer: ['new Magnetometer();'],
diff --git a/mediacapture-record/idlharness.html b/mediacapture-record/idlharness.html
index 95f60d7376024b..2da20a13171fdc 100644
--- a/mediacapture-record/idlharness.html
+++ b/mediacapture-record/idlharness.html
@@ -80,19 +80,24 @@
 
   </pre>
   <script>
-    var canvas = document.getElementById('canvas');
-    var context = canvas.getContext("2d");
-    context.fillStyle = "red";
-    context.fillRect(0, 0, 10, 10);
-    var stream = canvas.captureStream();
+    promise_test(async function() {
+      const dom = await fetch('/interfaces/dom.idl').then(r => r.text());
 
-    var idl_array = new IdlArray();
-    idl_array.add_untested_idls(document.getElementById("untested_idl").textContent);
-    idl_array.add_idls(document.getElementById("idl").textContent);
-    idl_array.add_objects({
-        MediaRecorder: [new MediaRecorder(stream)],
-      });
-    idl_array.test();
+      var canvas = document.getElementById('canvas');
+      var context = canvas.getContext("2d");
+      context.fillStyle = "red";
+      context.fillRect(0, 0, 10, 10);
+      var stream = canvas.captureStream();
+
+      var idl_array = new IdlArray();
+      idl_array.add_untested_idls(dom, { only: ['EventInit'] });
+      idl_array.add_untested_idls(document.getElementById("untested_idl").textContent);
+      idl_array.add_idls(document.getElementById("idl").textContent);
+      idl_array.add_objects({
+          MediaRecorder: [new MediaRecorder(stream)],
+        });
+      idl_array.test();
+    }, 'mediacapture-record interfaces');
   </script>
   <div id="log"></div>
 </body>
diff --git a/mediacapture-streams/MediaDevices-IDL-all.html b/mediacapture-streams/MediaDevices-IDL-all.html
index f6dfb361bb48f7..a793bedc78d66e 100644
--- a/mediacapture-streams/MediaDevices-IDL-all.html
+++ b/mediacapture-streams/MediaDevices-IDL-all.html
@@ -19,10 +19,11 @@ <h1 class="instructions">Description</h1>
     <script>
       'use strict';
 
-      function doIdlTest(idlText) {
+      function doIdlTest([dom, idlText]) {
         var idl_array = new IdlArray();
 
         // dummies
+        idl_array.add_untested_idls(dom, { only: ['Event', 'EventInit']});
         idl_array.add_untested_idls("interface Navigator {};");
         idl_array.add_untested_idls("interface EventTarget {};");
         idl_array.add_untested_idls("interface EventHandler {};");
@@ -35,10 +36,12 @@ <h1 class="instructions">Description</h1>
       }
 
       promise_test(() => {
-        return fetch('/interfaces/mediacapture-main.idl')
-          .then(response => response.text())
-          .then(doIdlTest);
-
+        return Promise.all(
+          [
+            '/interfaces/dom.idl',
+            '/interfaces/mediacapture-main.idl',
+          ].map(url => fetch(url).then(r => r.text())))
+            .then(doIdlTest);
       }, 'Test driver')
     </script>
   </body>
diff --git a/mediacapture-streams/MediaDevices-IDL-enumerateDevices.html b/mediacapture-streams/MediaDevices-IDL-enumerateDevices.html
index c2449ae6ce03c2..0d6c6c00bf5927 100644
--- a/mediacapture-streams/MediaDevices-IDL-enumerateDevices.html
+++ b/mediacapture-streams/MediaDevices-IDL-enumerateDevices.html
@@ -20,10 +20,10 @@ <h1 class="instructions">Description</h1>
 <script>
   "use strict";
 
-  function doIdlTest(idlText) {
+  function doIdlTest([dom, idlText]) {
     const MDI_idl = new IdlArray();
 
-    MDI_idl.add_untested_idls("interface Event {};");
+    MDI_idl.add_untested_idls(dom, { only: ['Event', 'EventInit'] });
     MDI_idl.add_untested_idls("interface EventTarget {};");
     MDI_idl.add_untested_idls("interface Navigator {};");
     MDI_idl.add_idls(idlText);
@@ -59,8 +59,11 @@ <h1 class="instructions">Description</h1>
   }
 
   promise_test(() => {
-    return fetch('/interfaces/mediacapture-main.idl')
-      .then(response => response.text())
+      return Promise.all(
+        [
+          '/interfaces/dom.idl',
+          '/interfaces/mediacapture-main.idl',
+        ].map(url => fetch(url).then(r => r.text())))
       .then(doIdlTest);
 
   }, "Test MediaDevices.enumerateDevices call and result. Types only.");
diff --git a/navigation-timing/nav2_idlharness.html b/navigation-timing/nav2_idlharness.html
index eb7d94b15a72d1..6d1a1249b91ab5 100644
--- a/navigation-timing/nav2_idlharness.html
+++ b/navigation-timing/nav2_idlharness.html
@@ -32,6 +32,7 @@
     [MeasureAs=PerformanceResourceTimingSizes] readonly attribute unsigned long long encodedBodySize;
     [MeasureAs=PerformanceResourceTimingSizes] readonly attribute unsigned long long decodedBodySize;
 };
+interface PerformanceEntry {};
 </pre>
 
 <pre id='idl'>
diff --git a/orientation-sensor/idlharness.https.html b/orientation-sensor/idlharness.https.html
index d1099b57864b80..c87d99f8085a0d 100644
--- a/orientation-sensor/idlharness.https.html
+++ b/orientation-sensor/idlharness.https.html
@@ -15,7 +15,7 @@
   const idl_array = new IdlArray();
   idl_array.add_untested_idls(dom);
   idl_array.add_untested_idls('interface EventHandler {};');
-  idl_array.add_idls(generic_sensor, { only: ['Sensor'] });
+  idl_array.add_idls(generic_sensor, { only: ['Sensor', 'SensorOptions'] });
   idl_array.add_idls(orientation_sensor);
   idl_array.add_objects({
     AbsoluteOrientationSensor: ['new AbsoluteOrientationSensor();'],
diff --git a/payment-handler/interfaces.https.any.js b/payment-handler/interfaces.https.any.js
index ccddf464d135ff..73679300f070c8 100644
--- a/payment-handler/interfaces.https.any.js
+++ b/payment-handler/interfaces.https.any.js
@@ -6,11 +6,11 @@
 // https://w3c.github.io/payment-handler/
 
 promise_test(async () => {
-  const text = await fetch('/interfaces/payment-handler.idl').then(response =>
-    response.text(),
-  );
+  const idl = await fetch('/interfaces/payment-handler.idl').then(r => r.text());
   const idlArray = new IdlArray();
-  idlArray.add_idls(text);
+  idlArray.add_idls(idl);
+  idlArray.add_untested_idls('interface ExtendableEvent {};');
+  idlArray.add_untested_idls('dictionary ExtendableEventInit {};');
   idlArray.test();
   done();
 }, 'Payment handler interfaces.');
diff --git a/pointerevents/extension/idlharness.html b/pointerevents/extension/idlharness.html
index d1bbdebda9252b..7da7fed4633404 100644
--- a/pointerevents/extension/idlharness.html
+++ b/pointerevents/extension/idlharness.html
@@ -48,8 +48,15 @@
 
 </pre>
 <script>
+promise_test(async function () {
+  const dom = await fetch('/interfaces/dom.idl').then(r => r.text());
+  const uievents = await fetch('/interfaces/uievents.idl').then(r => r.text());
+
   var idl_array = new IdlArray();
+  idl_array.add_untested_idls(dom, { only: ['EventInit'] });
+  idl_array.add_untested_idls(uievents, { only: ['UIEventInit', 'MouseEventInit', 'EventModifierInit'] });
   idl_array.add_untested_idls(document.getElementById("untested_idl").textContent);
   idl_array.add_idls(document.getElementById("idl").textContent);
   idl_array.test();
+}, 'pointerevents extension interfaces');
 </script>
diff --git a/pointerevents/idlharness.html b/pointerevents/idlharness.html
index 729d3573e87502..bdc7ad789ce758 100644
--- a/pointerevents/idlharness.html
+++ b/pointerevents/idlharness.html
@@ -91,14 +91,21 @@
 };
 </pre>
 <script>
-  var idl_array = new IdlArray();
-  idl_array.add_untested_idls(document.getElementById("untested_idl").textContent);
-  idl_array.add_idls(document.getElementById("idl").textContent);
+  promise_test(async function() {
+    const dom = await fetch('/interfaces/dom.idl').then(r => r.text());
+    const uievents = await fetch('/interfaces/uievents.idl').then(r => r.text());
 
-  // Note that I don't bother including Document here because there are still
-  // a bunch of differences between browsers around Document vs HTMLDocument.
-  idl_array.add_objects({
+    var idl_array = new IdlArray();
+    idl_array.add_untested_idls(dom, { only: ['EventInit'] });
+    idl_array.add_untested_idls(uievents, { only: ['UIEventInit', 'MouseEventInit', 'EventModifierInit'] });
+    idl_array.add_untested_idls(document.getElementById("untested_idl").textContent);
+    idl_array.add_idls(document.getElementById("idl").textContent);
+
+    // Note that I don't bother including Document here because there are still
+    // a bunch of differences between browsers around Document vs HTMLDocument.
+    idl_array.add_objects({
     Window: ["window"],
     Navigator: ["navigator"]});
-  idl_array.test();
+    idl_array.test();
+  }, 'pointerevents interfaces');
 </script>
diff --git a/remote-playback/idlharness.html b/remote-playback/idlharness.html
index bd9cbf6cc43e67..274771af684e4a 100644
--- a/remote-playback/idlharness.html
+++ b/remote-playback/idlharness.html
@@ -19,20 +19,32 @@ <h1>Remote Playback API IDL tests</h1>
 </pre>
 <script>
 "use strict"
-var idl_array = new IdlArray();
-function doTest(idl) {
-  idl_array.add_untested_idls(document.getElementById("untested_idl").textContent);
-  idl_array.add_idls(idl);
-  idl_array.add_objects({
-    HTMLVideoElement: [document.getElementById("media")],
-    RemotePlayback: [document.getElementById("media").remote]
-  });
-  idl_array.test();
-}
 
-promise_test(function() {
-  return fetch("/interfaces/remoteplayback.idl")
-      .then(response => response.text())
+promise_test(async function() {
+  var idl_array = new IdlArray();
+  function doTest([html, idl]) {
+    idl_array.add_untested_idls('interface Element {};');
+    idl_array.add_untested_idls(html, { only: [
+      'HTMLElement',
+      'HTMLOrSVGElement',
+      'GlobalEventHandlers',
+      'DocumentAndElementEventHandlers',
+      'ElementContentEditable',
+    ] });
+    idl_array.add_untested_idls(document.getElementById("untested_idl").textContent);
+    idl_array.add_idls(idl);
+    idl_array.add_objects({
+      HTMLVideoElement: [document.getElementById("media")],
+      RemotePlayback: [document.getElementById("media").remote]
+    });
+    idl_array.test();
+  }
+
+  return Promise.all(
+    [
+      "/interfaces/html.idl",
+      "/interfaces/remoteplayback.idl",
+    ].map(url => fetch(url).then(r => r.text())))
       .then(doTest);
 }, "Test driver");
 </script>
diff --git a/resources/idlharness.js b/resources/idlharness.js
index c3045c49f909c9..bfa8c2a2709b9c 100644
--- a/resources/idlharness.js
+++ b/resources/idlharness.js
@@ -683,6 +683,19 @@ IdlArray.prototype.test = function()
     }
     this["includes"] = {};
 
+    // Assert B defined for A : B
+    for (const member of Object.values(this.members).filter(m => m.base)) {
+        const lhs = member.name;
+        const rhs = member.base;
+        if (!(rhs in this.members)) throw new IdlHarnessError(`${lhs} inherits ${rhs}, but ${rhs} is undefined.`);
+        const lhs_is_interface = this.members[lhs] instanceof IdlInterface;
+        const rhs_is_interface = this.members[rhs] instanceof IdlInterface;
+        if (rhs_is_interface != lhs_is_interface) {
+            if (!lhs_is_interface) throw new IdlHarnessError(`${lhs} inherits ${rhs}, but ${lhs} is not an interface.`);
+            if (!rhs_is_interface) throw new IdlHarnessError(`${lhs} inherits ${rhs}, but ${rhs} is not an interface.`);
+        }
+    }
+
     Object.getOwnPropertyNames(this.members).forEach(function(memberName) {
         var member = this.members[memberName];
         if (!(member instanceof IdlInterface)) {
diff --git a/resources/test/tests/idlharness/IdlDictionary/get_inheritance_stack.html b/resources/test/tests/idlharness/IdlDictionary/get_inheritance_stack.html
index 3540afb3346e2f..98168ee119b428 100644
--- a/resources/test/tests/idlharness/IdlDictionary/get_inheritance_stack.html
+++ b/resources/test/tests/idlharness/IdlDictionary/get_inheritance_stack.html
@@ -29,6 +29,19 @@
         var A = idl.members["A"];
         assert_array_equals(A.get_inheritance_stack().map(d => d.name), ["A", "B", "C"]);
     }, 'should return an array of inherited dictionaries in order of inheritance, starting with itself.');
+
+    test(function () {
+      let i = new IdlArray();
+      i.add_untested_idls('dictionary A : B {};');
+      i.assert_throws(new IdlHarnessError('A inherits B, but B is undefined.'), i => i.test());
+    }, 'A : B with B undeclared should throw IdlHarnessError');
+
+    test(function () {
+      let i = new IdlArray();
+      i.add_untested_idls('dictionary A : B {};');
+      i.add_untested_idls('interface B {};');
+      i.assert_throws(new IdlHarnessError('A inherits B, but A is not an interface.'), i => i.test());
+    }, 'dictionary A : B with B interface should throw IdlHarnessError');
 </script>
 </body>
 </html>
diff --git a/resources/test/tests/idlharness/IdlInterface/test_primary_interface_of_undefined.html b/resources/test/tests/idlharness/IdlInterface/test_primary_interface_of_undefined.html
new file mode 100644
index 00000000000000..0031558ad42ce5
--- /dev/null
+++ b/resources/test/tests/idlharness/IdlInterface/test_primary_interface_of_undefined.html
@@ -0,0 +1,29 @@
+<!DOCTYPE HTML>
+<html>
+
+<head>
+  <title>idlharness test_primary_interface_of_undefined</title>
+</head>
+
+<body>
+  <script src="/resources/testharness.js"></script>
+  <script src="/resources/WebIDLParser.js"></script>
+  <script src="/resources/idlharness.js"></script>
+  <script>
+    'use strict';
+    test(function () {
+      let i = new IdlArray();
+      i.add_untested_idls('interface A : B {};');
+      i.assert_throws(new IdlHarnessError('A inherits B, but B is undefined.'), i => i.test());
+    }, 'A : B with B undeclared should throw IdlHarnessError');
+
+    test(function () {
+      let i = new IdlArray();
+      i.add_untested_idls('interface A : B {};');
+      i.add_untested_idls('dictionary B {};');
+      i.assert_throws(new IdlHarnessError('A inherits B, but B is not an interface.'), i => i.test());
+    }, 'interface A : B with B dictionary should throw IdlHarnessError');
+  </script>
+</body>
+
+</html>
diff --git a/service-workers/service-worker/interfaces-window.https.html b/service-workers/service-worker/interfaces-window.https.html
index 307472444d63e0..54f83f202c3131 100644
--- a/service-workers/service-worker/interfaces-window.https.html
+++ b/service-workers/service-worker/interfaces-window.https.html
@@ -11,9 +11,11 @@
 
 promise_test(async (t) => {
   var idlArray = new IdlArray();
-  let serviceWorkerIdl = await fetch('/interfaces/ServiceWorker.idl').then(r => r.text());
+  const dom = await fetch('/interfaces/dom.idl').then(r => r.text());
+  const serviceWorkerIdl = await fetch('/interfaces/ServiceWorker.idl').then(r => r.text());
 
   idlArray.add_untested_idls(idls.untested);
+  idlArray.add_untested_idls(dom, { only: ['EventTarget'] });
   idlArray.add_idls(serviceWorkerIdl, { only: [
     'ServiceWorkerGlobalScope',
     'Client',
diff --git a/service-workers/service-worker/resources/interfaces-worker.sub.js b/service-workers/service-worker/resources/interfaces-worker.sub.js
index e8147f73fca649..29c859bb91456a 100644
--- a/service-workers/service-worker/resources/interfaces-worker.sub.js
+++ b/service-workers/service-worker/resources/interfaces-worker.sub.js
@@ -7,9 +7,11 @@ importScripts('/resources/idlharness.js');
 
 promise_test(async (t) => {
   var idlArray = new IdlArray();
-  let serviceWorkerIdl = await fetch('/interfaces/ServiceWorker.idl').then(r => r.text());
+  const dom = await fetch('/interfaces/dom.idl').then(r => r.text());
+  const serviceWorkerIdl = await fetch('/interfaces/ServiceWorker.idl').then(r => r.text());
 
   idlArray.add_untested_idls(idls.untested);
+  idlArray.add_untested_idls(dom, { only: ['EventTarget'] });
   idlArray.add_idls(serviceWorkerIdl, { only: [
     'ServiceWorkerGlobalScope',
     'Client',
diff --git a/webaudio/idlharness.https.html b/webaudio/idlharness.https.html
index aed91706eb9ee6..09ec2c430bccde 100644
--- a/webaudio/idlharness.https.html
+++ b/webaudio/idlharness.https.html
@@ -10,13 +10,16 @@
 'use strict';
 
 promise_test(async t => {
-  const [html, dom, mediacapture, webaudio] = await Promise.all([
+  const [html, dom, uievents, mediacapture, webaudio] = await Promise.all([
     // Needed for EventTarget, HTMLMediaElement
     '/interfaces/html.idl',
 
     // Needed for Event, EventListener
     '/interfaces/dom.idl',
 
+    // Needed for MouseEvent
+    '/interfaces/uievents.idl',
+
     // Needed for MediaStream, MediaStreamTrack
     '/interfaces/mediacapture-main.idl',
 
@@ -28,7 +31,15 @@
   // Dependencies of HTML
   idl_array.add_untested_idls('interface LinkStyle {};');
   idl_array.add_untested_idls('interface SVGElement {};');
+  idl_array.add_untested_idls('interface WorkletGlobalScope {};');
   idl_array.add_untested_idls(html);
+  idl_array.add_untested_idls(uievents, { only: [
+    'MouseEvent',
+    'MouseEventInit',
+    'EventModifierInit',
+    'UIEvent',
+    'UIEventInit',
+  ]});
 
   idl_array.add_untested_idls(dom);
   idl_array.add_untested_idls(mediacapture);
diff --git a/webaudio/the-audio-api/the-delaynode-interface/idl-test.html b/webaudio/the-audio-api/the-delaynode-interface/idl-test.html
index 5922b96f6975e4..eb42a4a003c893 100644
--- a/webaudio/the-audio-api/the-delaynode-interface/idl-test.html
+++ b/webaudio/the-audio-api/the-delaynode-interface/idl-test.html
@@ -138,8 +138,11 @@
   <div id="log"></div>
 
   <script>
-(function() {
+promise_test(async function() {
+  const webAudioApi = await fetch('/interfaces/web-audio-api.idl').then(r => r.text());
+
   var idl_array = new IdlArray();
+  idl_array.add_untested_idls(webAudioApi, { only: ['AudioNodeOptions']});
   idl_array.add_untested_idls(document.getElementById("event-target-idl").textContent);
   idl_array.add_untested_idls(document.getElementById("base-audio-context-idl").textContent);
   idl_array.add_untested_idls(document.getElementById("audio-node-idl").textContent);
@@ -150,7 +153,7 @@
 
   idl_array.add_objects({DelayNode: ["delay_node"]});
   idl_array.test();
-})();
+}, 'webaudio Delay interfaces');
   </script>
 </body>
 </html>
diff --git a/webaudio/the-audio-api/the-gainnode-interface/idl-test.html b/webaudio/the-audio-api/the-gainnode-interface/idl-test.html
index 7ad8bc90364bf7..69606c977eda42 100644
--- a/webaudio/the-audio-api/the-gainnode-interface/idl-test.html
+++ b/webaudio/the-audio-api/the-gainnode-interface/idl-test.html
@@ -136,8 +136,11 @@
   <div id="log"></div>
 
   <script>
-(function() {
+promise_test(async function () {
+  const webAudioApi = await fetch('/interfaces/web-audio-api.idl').then(r => r.text());
+
   var idl_array = new IdlArray();
+  idl_array.add_untested_idls(webAudioApi, { only: ['AudioNodeOptions'] });
   idl_array.add_untested_idls(document.getElementById("event-target-idl").textContent);
   idl_array.add_untested_idls(document.getElementById("base-audio-context-idl").textContent);
   idl_array.add_untested_idls(document.getElementById("audio-node-idl").textContent);
@@ -148,7 +151,7 @@
 
   idl_array.add_objects({GainNode: ["gain_node"]});
   idl_array.test();
-})();
+}, 'webaudio Gain interfaces');
   </script>
 </body>
 </html>
diff --git a/webauthn/interfaces.https.any.js b/webauthn/interfaces.https.any.js
index bd5f9dc4a285cc..22766e650ce142 100644
--- a/webauthn/interfaces.https.any.js
+++ b/webauthn/interfaces.https.any.js
@@ -20,6 +20,7 @@ promise_test(async () => {
   idlArray.add_untested_idls('interface CredentialCreationOptions {};');
   idlArray.add_untested_idls('interface CredentialRequestOptions {};');
   idlArray.add_untested_idls("interface Navigator { };");
+  idlArray.add_untested_idls("interface Credential { };");
   // TODO: change to "tested" for real browsers?
   idlArray.add_untested_idls("partial interface Navigator { readonly attribute WebAuthentication authentication; };");
   idlArray.add_objects({
diff --git a/webstorage/idlharness.html b/webstorage/idlharness.html
index cd880a33f03476..4204344e165e06 100644
--- a/webstorage/idlharness.html
+++ b/webstorage/idlharness.html
@@ -18,12 +18,6 @@ <h1>Web Storage IDL tests</h1>
 [Global=Window, Exposed=Window]
 interface Window {
 };
-
-interface Event {
-};
-
-interface EventInit {
-};
 </pre>
 
 <pre id='idl'>
@@ -65,16 +59,21 @@ <h1>Web Storage IDL tests</h1>
 
 <script>
 
-(function() {
+promise_test(async function() {
+  const dom = await fetch('/interfaces/dom.idl').then(r => r.text());
+  const html = await fetch('/interfaces/html.idl').then(r => r.text());
+
   var idl_array = new IdlArray();
 
+  idl_array.add_untested_idls(dom, { only: ['Event', 'EventInit'] });
+  idl_array.add_untested_idls(html, { only: ['EventStorageInit'] });
   idl_array.add_untested_idls(document.getElementById("untested_idl").textContent);
   idl_array.add_idls(document.getElementById("idl").textContent);
 
   idl_array.add_objects({Storage: ["window.localStorage"]});
 
   idl_array.test();
-})();
+}, 'webstorage interfaces');
 
 </script>
 </body>