diff --git a/build-system/amp.extern.js b/build-system/amp.extern.js
index 7fd09eea9b60e..d4cd8e76f7517 100644
--- a/build-system/amp.extern.js
+++ b/build-system/amp.extern.js
@@ -104,6 +104,7 @@ var AmpElement;
 var AccessService = function() {};
 /** @constructor */
 var UserNotificationManager = function() {};
+UserNotificationManager.prototype.get;
 /** @constructor */
 var Cid = function() {};
 /** @constructor */
@@ -136,3 +137,48 @@ FB.init;
 var amp;
 amp.validator;
 amp.validator.validateUrlAndLog = function(string, doc, filter) {}
+
+// Temporary Access types (delete when amp-access is compiled
+// for type checking).
+var Activity;
+Activity.prototype.getTotalEngagedTime = function() {};
+var AccessService;
+AccessService.prototype.getAccessReaderId = function() {};
+AccessService.prototype.getAuthdataField = function(field) {};
+// Same for amp-analytics
+/**
+ * The "get CID" parameters.
+ * - createCookieIfNotPresent: Whether CID is allowed to create a cookie when.
+ *   Default value is `false`.
+ * @typedef {{
+ *   scope: string,
+ *   createCookieIfNotPresent: (boolean|undefined),
+ * }}
+ */
+var GetCidDef;
+var Cid;
+/**
+ * @param {string|!GetCidDef} externalCidScope Name of the fallback cookie
+ *     for the case where this doc is not served by an AMP proxy. GetCidDef
+ *     structure can also instruct CID to create a cookie if one doesn't yet
+ *     exist in a non-proxy case.
+ * @param {!Promise} consent Promise for when the user has given consent
+ *     (if deemed necessary by the publisher) for use of the client
+ *     identifier.
+ * @param {!Promise=} opt_persistenceConsent Dedicated promise for when
+ *     it is OK to persist a new tracking identifier. This could be
+ *     supplied ONLY by the code that supplies the actual consent
+ *     cookie.
+ *     If this is given, the consent param should be a resolved promise
+ *     because this call should be only made in order to get consent.
+ *     The consent promise passed to other calls should then itself
+ *     depend on the opt_persistenceConsent promise (and the actual
+ *     consent, of course).
+ * @return {!Promise<?string>} A client identifier that should be used
+ *      within the current source origin and externalCidScope. Might be
+ *      null if no identifier was found or could be made.
+ *      This promise may take a long time to resolve if consent isn't
+ *      given.
+ */
+Cid.prototype.get = function(
+    externalCidScope, consent, opt_persistenceConsent) {}
diff --git a/build-system/runner/dist/runner.jar b/build-system/runner/dist/runner.jar
index 5c24dda0b9dae..75ffa99c75619 100644
Binary files a/build-system/runner/dist/runner.jar and b/build-system/runner/dist/runner.jar differ
diff --git a/build-system/runner/src/org/ampproject/AmpCodingConvention.java b/build-system/runner/src/org/ampproject/AmpCodingConvention.java
index 0ca1a3e211678..6fdb01c949caf 100644
--- a/build-system/runner/src/org/ampproject/AmpCodingConvention.java
+++ b/build-system/runner/src/org/ampproject/AmpCodingConvention.java
@@ -47,7 +47,9 @@ public AmpCodingConvention(CodingConvention convention) {
         new AssertionFunctionSpec("user.assert", JSType.TRUTHY),
         new AssertionFunctionSpec("dev.assert", JSType.TRUTHY),
         new AssertionFunctionSpec("Log$$module$src$log.prototype.assert", JSType.TRUTHY),
-        new AssertFunctionByTypeName("Log$$module$src$log.prototype.assertElement", "Element")
+        new AssertFunctionByTypeName("Log$$module$src$log.prototype.assertElement", "Element"),
+        new AssertFunctionByTypeName("Log$$module$src$log.prototype.assertString", "string"),
+        new AssertFunctionByTypeName("Log$$module$src$log.prototype.assertNumber", "number")
     );
   }
 
diff --git a/build-system/runner/src/org/ampproject/AmpCommandLineRunner.java b/build-system/runner/src/org/ampproject/AmpCommandLineRunner.java
index c7f0db1b80f17..ae993a8e6ee5f 100644
--- a/build-system/runner/src/org/ampproject/AmpCommandLineRunner.java
+++ b/build-system/runner/src/org/ampproject/AmpCommandLineRunner.java
@@ -48,8 +48,8 @@ public class AmpCommandLineRunner extends CommandLineRunner {
    */
   ImmutableSet<String> suffixTypes = ImmutableSet.of(
       "dev.fine");
-  
-  
+
+
   ImmutableMap<String, Node> assignmentReplacements = ImmutableMap.of(
       "IS_DEV",
       IR.falseNode());
@@ -98,6 +98,7 @@ protected AmpCommandLineRunner(String[] args) {
   protected CompilerOptions createTypeCheckingOptions() {
     CompilerOptions options = super.createOptions();
     options.setCheckTypes(true);
+    options.setInferTypes(true);
     return options;
   }
 
diff --git a/build-system/tasks/compile.js b/build-system/tasks/compile.js
index aafe53229acf4..4b79f84a35c4b 100644
--- a/build-system/tasks/compile.js
+++ b/build-system/tasks/compile.js
@@ -224,6 +224,7 @@ function compile(entryModuleFilename, outputDir,
           '3p/environment.js',
           'src/document-state.js',
         ],
+        jscomp_error: [],
       }
     };
 
@@ -232,7 +233,8 @@ function compile(entryModuleFilename, outputDir,
       // Don't modify compilation_level to a lower level since
       // it won't do strict type checking if its whitespace only.
       compilerOptions.compilerFlags.define.push('TYPECHECK_ONLY=true');
-      compilerOptions.compilerFlags.jscomp_error = 'checkTypes';
+      compilerOptions.compilerFlags.jscomp_error.push(
+          'checkTypes', 'accessControls', 'const', 'constantProperty');
     }
     if (argv.pseudo_names) {
       compilerOptions.compilerFlags.define.push('PSEUDO_NAMES=true');
diff --git a/build-system/tasks/presubmit-checks.js b/build-system/tasks/presubmit-checks.js
index 9f53709dd714b..bf57d121b60a2 100644
--- a/build-system/tasks/presubmit-checks.js
+++ b/build-system/tasks/presubmit-checks.js
@@ -340,6 +340,7 @@ var forbiddenTerms = {
   'getAccessReaderId': {
     message: requiresReviewPrivacy,
     whitelist: [
+      'build-system/amp.extern.js',
       'extensions/amp-access/0.1/amp-access.js',
       'src/service/url-replacements-impl.js',
     ]
@@ -347,6 +348,7 @@ var forbiddenTerms = {
   'getAuthdataField': {
     message: requiresReviewPrivacy,
     whitelist: [
+      'build-system/amp.extern.js',
       'extensions/amp-access/0.1/amp-access.js',
       'src/service/url-replacements-impl.js',
     ]
diff --git a/builtins/amp-video.js b/builtins/amp-video.js
index d04a16088c2b3..aca95fa850b51 100644
--- a/builtins/amp-video.js
+++ b/builtins/amp-video.js
@@ -20,6 +20,7 @@ import {isLayoutSizeDefined} from '../src/layout';
 import {loadPromise} from '../src/event-helper';
 import {registerElement} from '../src/custom-element';
 import {getMode} from '../src/mode';
+import {dev} from '../src/log';
 
 /**
  * @param {!Window} win Destination window for the new element.
@@ -36,7 +37,7 @@ export function installVideo(win) {
 
     /** @override */
     buildCallback() {
-      /** @private @const {!HTMLVideoElement} */
+      /** @private @const {!Element} */
       this.video_ = this.element.ownerDocument.createElement('video');
 
       const posterAttr = this.element.getAttribute('poster');
@@ -82,7 +83,8 @@ export function installVideo(win) {
           return;
         }
         if (child.getAttribute && child.getAttribute('src')) {
-          assertHttpsUrl(child.getAttribute('src'), child);
+          assertHttpsUrl(child.getAttribute('src'),
+              dev().assertElement(child));
         }
         this.video_.appendChild(child);
       });
diff --git a/extensions/amp-apester-media/0.1/test/test-amp-apester-media.js b/extensions/amp-apester-media/0.1/test/test-amp-apester-media.js
index 5ebfd31a79a7a..aff54183d759f 100644
--- a/extensions/amp-apester-media/0.1/test/test-amp-apester-media.js
+++ b/extensions/amp-apester-media/0.1/test/test-amp-apester-media.js
@@ -72,6 +72,7 @@ describe('amp-apester-media', () => {
         media.setAttribute(key, attributes[key]);
 
       }
+      media.setAttribute('width', '600');
       media.setAttribute('height', '390');
       //todo test width?
       if (opt_responsive) {
diff --git a/gulpfile.js b/gulpfile.js
index 3d69af5018679..636f54981e9e3 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -138,11 +138,7 @@ function compile(watch, shouldMinify, opt_preventRemoveAndMakeDir,
     preventRemoveAndMakeDir: opt_preventRemoveAndMakeDir,
     externs: ['ads/ads.extern.js',],
   });
-  // The main binary does not yet compile successfully with type checking
-  // turned on. Skip for now.
-  if (opt_checkTypes && !argv.more) {
-    return;
-  }
+
   // For compilation with babel we start with the amp-babel entry point,
   // but then rename to the amp.js which we've been using all along.
   compileJs('./src/', 'amp-babel.js', './dist', {
@@ -163,6 +159,10 @@ function compile(watch, shouldMinify, opt_preventRemoveAndMakeDir,
         's.animation="none";' +
         's.WebkitAnimation="none;"},1000);throw e};'
   });
+  if (opt_checkTypes) {
+    // We don't rerun type check for the shadow entry point for now.
+    return;
+  }
   // Entry point for shadow runtime.
   compileJs('./src/', 'amp-shadow-babel.js', './dist', {
     toName: 'amp-shadow.js',
@@ -344,11 +344,12 @@ function checkTypes() {
     checkTypes: true,
     preventRemoveAndMakeDir: true,
   });
-  buildSw({
+  // Temporarily turned off due to unknown type warnings.
+  /*buildSw({
     minify: true,
     checkTypes: true,
     preventRemoveAndMakeDir: true,
-  });
+  });*/
   buildExperiments({
     minify: true,
     checkTypes: true,
@@ -356,7 +357,6 @@ function checkTypes() {
   });
   compile(false, true, /* opt_preventRemoveAndMakeDir*/ true,
       /* check types */ true);
-  // These are not turned on on Travis.
 }
 
 /**
diff --git a/src/access-service.js b/src/access-service.js
index 07e806d0b6418..2775591f671fc 100644
--- a/src/access-service.js
+++ b/src/access-service.js
@@ -26,7 +26,8 @@ import {
  * @return {!Promise<!AccessService>}
  */
 export function accessServiceFor(win) {
-  return getElementService(win, 'access', 'amp-access');
+  return /** @type {!Promise<!AccessService>} */ (
+        getElementService(win, 'access', 'amp-access'));
 }
 
 /**
@@ -36,5 +37,6 @@ export function accessServiceFor(win) {
  * @return {!Promise<?AccessService>}
  */
 export function accessServiceForOrNull(win) {
-  return getElementServiceIfAvailable(win, 'access', 'amp-access');
+  return /** @type {!Promise<?AccessService>} */ (
+      getElementServiceIfAvailable(win, 'access', 'amp-access'));
 }
diff --git a/src/activity.js b/src/activity.js
index e8390b48bf294..bc726c39e0f66 100644
--- a/src/activity.js
+++ b/src/activity.js
@@ -21,5 +21,6 @@ import {getElementService} from './element-service';
  * @return {!Promise<!Activity>}
  */
 export function activityFor(win) {
-  return getElementService(win, 'activity', 'amp-analytics');
+  return /** @type {!Promise<!Activity>} */ (
+      getElementService(win, 'activity', 'amp-analytics'));
 };
diff --git a/src/animation.js b/src/animation.js
index c743a901f75d8..a191d5d23f926 100644
--- a/src/animation.js
+++ b/src/animation.js
@@ -73,11 +73,13 @@ export class Animation {
    * Sets the default curve for the animation. Each segment is allowed to have
    * its own curve, but this curve will be used if a segment doesn't specify
    * its own.
-   * @param {!./curve.CurveDef|string} curve
+   * @param {!./curve.CurveDef|string|undefined} curve
    * @return {!Animation}
    */
   setCurve(curve) {
-    this.curve_ = getCurve(curve);
+    if (curve) {
+      this.curve_ = getCurve(curve);
+    }
     return this;
   }
 
@@ -127,7 +129,8 @@ export class Animation {
  * semantics of a Promise and signal when the animation completed or failed.
  * Additionally, it exposes the method "halt" which allows to stop/reset the
  * animation.
- * @implements {IThenable}
+ * // TODO(@cramforce) Actually fully implement.
+ * implements {IThenable}
  */
 class AnimationPlayer {
 
diff --git a/src/base-element.js b/src/base-element.js
index 2b7f1964edf3c..4dc2f864bbe0a 100644
--- a/src/base-element.js
+++ b/src/base-element.js
@@ -143,7 +143,7 @@ export class BaseElement {
     /** @private {!Object<string, function(!./service/action-impl.ActionInvocation)>} */
     this.actionMap_ = this.win.Object.create(null);
 
-    /** @protected {!./preconnect.Preconnect} */
+    /** @public {!./preconnect.Preconnect} */
     this.preconnect = preconnectFor(this.win);
   }
 
@@ -164,13 +164,13 @@ export class BaseElement {
 
   /**
    * DO NOT CALL. Retained for backward compat during rollout.
-   * @protected @return {!Window}
+   * @public @return {!Window}
    */
   getWin() {
     return this.win;
   }
 
-  /** @protected @return {!./service/vsync-impl.Vsync} */
+  /** @public @return {!./service/vsync-impl.Vsync} */
   getVsync() {
     return vsyncFor(this.win);
   }
@@ -180,7 +180,7 @@ export class BaseElement {
    * layout is not yet known. A `0` value indicates that the element is not
    * visible.
    * @return {number}
-   * @protected
+   * @public
    */
   getLayoutWidth() {
     return this.layoutWidth_;
@@ -192,7 +192,7 @@ export class BaseElement {
    * supported.
    * @param {!Layout} layout
    * @return {boolean}
-   * @protected
+   * @public
    */
   isLayoutSupported(layout) {
     return layout == Layout.NODISPLAY;
@@ -202,7 +202,7 @@ export class BaseElement {
    * Intended to be implemented by subclasses. Tests whether the element
    * requires fixed positioning.
    * @return {boolean}
-   * @protected
+   * @public
    */
   isAlwaysFixed() {
     return false;
@@ -267,8 +267,9 @@ export class BaseElement {
    * Called by the framework to give the element a chance to preconnect to
    * hosts and prefetch resources it is likely to need. May be called
    * multiple times because connections can time out.
+   * @param {boolean=} opt_onLayout
    */
-  preconnectCallback() {
+  preconnectCallback(opt_onLayout) {
     // Subclasses may override.
   }
 
@@ -357,7 +358,7 @@ export class BaseElement {
    * The default behavior of this method is to hide the placeholder. However,
    * a subclass may choose to hide placeholder earlier or not hide it at all.
    *
-   * @protected
+   * @public
    */
   firstLayoutCompleted() {
     this.togglePlaceholder(false);
@@ -420,7 +421,7 @@ export class BaseElement {
    * Registers the action handler for the method with the specified name.
    * @param {string} method
    * @param {function(!./service/action-impl.ActionInvocation)} handler
-   * @protected
+   * @public
    */
   registerAction(method, handler) {
     this.actionMap_[method] = handler;
@@ -469,7 +470,7 @@ export class BaseElement {
    * to the given element.
    * @param  {!Array<string>} attributes
    * @param  {!Element} element
-   * @protected @final
+   * @public @final
    */
   propagateAttributes(attributes, element) {
     for (let i = 0; i < attributes.length; i++) {
@@ -484,7 +485,7 @@ export class BaseElement {
   /**
    * Returns an optional placeholder element for this custom element.
    * @return {?Element}
-   * @protected @final
+   * @public @final
    */
   getPlaceholder() {
     return this.element.getPlaceholder();
@@ -493,7 +494,7 @@ export class BaseElement {
   /**
    * Hides or shows the placeholder, if available.
    * @param {boolean} state
-   * @protected @final
+   * @public @final
    */
   togglePlaceholder(state) {
     this.element.togglePlaceholder(state);
@@ -502,7 +503,7 @@ export class BaseElement {
   /**
    * Returns an optional fallback element for this custom element.
    * @return {?Element}
-   * @protected @final
+   * @public @final
    */
   getFallback() {
     return this.element.getFallback();
@@ -512,7 +513,7 @@ export class BaseElement {
    * Hides or shows the fallback, if available. This function must only
    * be called inside a mutate context.
    * @param {boolean} state
-   * @protected @final
+   * @public @final
    */
   toggleFallback(state) {
     this.element.toggleFallback(state);
@@ -521,7 +522,7 @@ export class BaseElement {
   /**
    * Returns an optional overflow element for this custom element.
    * @return {?Element}
-   * @protected @final
+   * @public @final
    */
   getOverflowElement() {
     return this.element.getOverflowElement();
@@ -532,7 +533,7 @@ export class BaseElement {
    * that could have been added for markup. These nodes can include Text,
    * Comment and other child nodes.
    * @return {!Array<!Node>}
-   * @protected @final
+   * @public @final
    */
   getRealChildNodes() {
     return this.element.getRealChildNodes();
@@ -542,7 +543,7 @@ export class BaseElement {
    * Returns the original children of the custom element without any service
    * nodes that could have been added for markup.
    * @return {!Array<!Element>}
-   * @protected @final
+   * @public @final
    */
   getRealChildren() {
     return this.element.getRealChildren();
@@ -558,7 +559,7 @@ export class BaseElement {
    *
    * @param {!Element} element
    * @param {boolean=} opt_replacedContent
-   * @protected @final
+   * @public @final
    */
   applyFillContent(element, opt_replacedContent) {
     element.classList.add('-amp-fill-content');
@@ -589,7 +590,7 @@ export class BaseElement {
    * specified. Resource manager will perform the actual layout based on the
    * priority of this element and its children.
    * @param {!Element|!Array<!Element>} elements
-   * @protected
+   * @public
    */
   scheduleLayout(elements) {
     this.element.getResources().scheduleLayout(this.element, elements);
@@ -597,7 +598,7 @@ export class BaseElement {
 
   /**
    * @param {!Element|!Array<!Element>} elements
-   * @protected
+   * @public
    */
   schedulePause(elements) {
     this.element.getResources().schedulePause(this.element, elements);
@@ -605,7 +606,7 @@ export class BaseElement {
 
   /**
    * @param {!Element|!Array<!Element>} elements
-   * @protected
+   * @public
    */
   scheduleResume(elements) {
     this.element.getResources().scheduleResume(this.element, elements);
@@ -616,8 +617,7 @@ export class BaseElement {
    * specified. Resource manager will perform the actual preload based on the
    * priority of this element and its children.
    * @param {!Element|!Array<!Element>} elements
-   * @param {boolean} inLocalViewport
-   * @protected
+   * @public
    */
   schedulePreload(elements) {
     this.element.getResources().schedulePreload(this.element, elements);
@@ -625,7 +625,7 @@ export class BaseElement {
 
   /**
    * @param {!Element|!Array<!Element>} elements
-   * @protected
+   * @public
    */
   scheduleUnlayout(elements) {
     this.element.getResources()./*OK*/scheduleUnlayout(this.element, elements);
@@ -637,7 +637,7 @@ export class BaseElement {
    * based on the state of these elements and their parent subtree.
    * @param {!Element|!Array<!Element>} elements
    * @param {boolean} inLocalViewport
-   * @protected
+   * @public
    */
   updateInViewport(elements, inLocalViewport) {
     this.element.getResources().updateInViewport(
@@ -649,7 +649,7 @@ export class BaseElement {
    * value. The runtime will schedule this request and attempt to process it
    * as soon as possible.
    * @param {number} newHeight
-   * @protected
+   * @public
    */
   changeHeight(newHeight) {
     this.element.getResources()./*OK*/changeSize(
@@ -668,7 +668,7 @@ export class BaseElement {
    * The promise is resolved if the height is successfully updated.
    * @param {number} newHeight
    * @return {!Promise}
-   * @protected
+   * @public
    */
   attemptChangeHeight(newHeight) {
     return this.element.getResources().attemptChangeSize(
@@ -688,7 +688,7 @@ export class BaseElement {
   * @param {number|undefined} newHeight
   * @param {number|undefined} newWidth
   * @return {!Promise}
-  * @protected
+  * @public
   */
   attemptChangeSize(newHeight, newWidth) {
     return this.element.getResources().attemptChangeSize(
@@ -725,7 +725,7 @@ export class BaseElement {
 
   /**
    * Requests full overlay mode from the viewer.
-   * @protected
+   * @public
    * @deprecated Use `Viewport.enterLightboxMode`.
    * TODO(dvoytenko, #3406): Remove as deprecated.
    */
@@ -735,7 +735,7 @@ export class BaseElement {
 
   /**
    * Requests to cancel full overlay mode from the viewer.
-   * @protected
+   * @public
    * @deprecated Use `Viewport.leaveLightboxMode`.
    * TODO(dvoytenko, #3406): Remove as deprecated.
    */
@@ -766,7 +766,7 @@ export class BaseElement {
    * more expensive style reads should now be cheap.
    * This may currently not work with extended elements. Please file
    * an issue if that is required.
-   * @protected
+   * @public
    */
   onLayoutMeasure() {}
 };
diff --git a/src/cid.js b/src/cid.js
index 1ae14d39cba0d..369c6a514044b 100644
--- a/src/cid.js
+++ b/src/cid.js
@@ -28,7 +28,8 @@ import {
  * @return {!Promise<!Cid>}
  */
 export function cidFor(window) {
-  return getElementService(window, 'cid', 'amp-analytics');
+  return /** @type {!Promise<!Cid>} */ (
+      getElementService(window, 'cid', 'amp-analytics'));
 };
 
 /**
@@ -38,5 +39,6 @@ export function cidFor(window) {
  * @return {!Promise<?Cid>}
  */
 export function cidForOrNull(window) {
-  return getElementServiceIfAvailable(window, 'cid', 'amp-analytics');
+  return /** @type {!Promise<?Cid>} */ (
+      getElementServiceIfAvailable(window, 'cid', 'amp-analytics'));
 };
diff --git a/src/custom-element.js b/src/custom-element.js
index bddb67056a182..220836dc91fdc 100644
--- a/src/custom-element.js
+++ b/src/custom-element.js
@@ -98,7 +98,7 @@ const UpgradeState = {
  */
 export function upgradeOrRegisterElement(win, name, toClass) {
   if (!knownElements[name]) {
-    registerElement(win, name, toClass);
+    registerElement(win, name, /** @type {!Function} */ (toClass));
     return;
   }
   user().assert(knownElements[name] == ElementStub,
@@ -187,7 +187,7 @@ export function stubElementIfNotKnown(win, name) {
 
 /**
  * Applies layout to the element. Visible for testing only.
- * @param {!AmpElement} element
+ * @param {!Element} element
  */
 export function applyLayout_(element) {
   const layoutAttr = element.getAttribute('layout');
@@ -271,10 +271,10 @@ export function applyLayout_(element) {
   if (layout == Layout.NODISPLAY) {
     element.style.display = 'none';
   } else if (layout == Layout.FIXED) {
-    element.style.width = width;
-    element.style.height = height;
+    element.style.width = dev().assertString(width);
+    element.style.height = dev().assertString(height);
   } else if (layout == Layout.FIXED_HEIGHT) {
-    element.style.height = height;
+    element.style.height = dev().assertString(height);
   } else if (layout == Layout.RESPONSIVE) {
     const sizer = element.ownerDocument.createElement('i-amp-sizer');
     sizer.style.display = 'block';
@@ -336,7 +336,7 @@ class AmpElement {
  *
  * @param {!Window} win The window in which to register the elements.
  * @param {string} name Name of the custom element
- * @param {function(new:./base-element.BaseElement, !Element)} opt_implementationClass For
+ * @param {function(new:./base-element.BaseElement, !Element)=} opt_implementationClass For
  *     testing only.
  * @return {!Object} Prototype of element.
  */
@@ -506,7 +506,7 @@ function createBaseAmpElementProto(win) {
 
   /**
    * Completes the upgrade of the element with the provided implementation.
-   * @param {./base-element.BaseElement} newImpl
+   * @param {!./base-element.BaseElement} newImpl
    * @final @private @this {!Element}
    */
   ElementProto.completeUpgrade_ = function(newImpl) {
@@ -863,7 +863,7 @@ function createBaseAmpElementProto(win) {
 
   /**
    * Whether the element should ever render when it is not in viewport.
-   * @return {boolean}
+   * @return {boolean|number}
    * @final @this {!Element}
    */
   ElementProto.renderOutsideViewport = function() {
@@ -1056,7 +1056,7 @@ function createBaseAmpElementProto(win) {
 
   /**
    * Called every time an owned AmpElement collapses itself.
-   * @param {!AmpElement} unusedElement
+   * @param {!AmpElement} element
    */
   ElementProto.collapsedCallback = function(element) {
     this.implementation_.collapsedCallback(element);
@@ -1373,8 +1373,6 @@ export function registerElement(win, name, implementationClass) {
  * @param {!Window} win The window in which to register the elements.
  * @param {string} aliasName Additional name for an existing custom element.
  * @param {string} sourceName Name of an existing custom element
- * @param {Object} state Optional map to be merged into the prototype
- *                 to override the original state with new default values
  */
 export function registerElementAlias(win, aliasName, sourceName) {
   const implementationClass = knownElements[sourceName];
diff --git a/src/document-click.js b/src/document-click.js
index aaabc0b65cdbc..09a95da2a9138 100644
--- a/src/document-click.js
+++ b/src/document-click.js
@@ -120,7 +120,7 @@ export function onDocumentElementClick_(e, viewport, history, isIosSafari) {
     return;
   }
 
-  const target = closestByTag(e.target, 'A');
+  const target = closestByTag(dev().assertElement(e.target), 'A');
   if (!target) {
     return;
   }
diff --git a/src/document-info.js b/src/document-info.js
index 2b7825e35789e..14807df712fd3 100644
--- a/src/document-info.js
+++ b/src/document-info.js
@@ -42,20 +42,22 @@ export let DocumentInfoDef;
  * @return {!DocumentInfoDef} Info about the doc
  */
 export function documentInfoForDoc(nodeOrDoc) {
-  return getServiceForDoc(nodeOrDoc, 'documentInfo', ampdoc => {
-    const url = ampdoc.getUrl();
-    const sourceUrl = getSourceUrl(url);
-    const rootNode = ampdoc.getRootNode();
-    let canonicalUrl = rootNode && rootNode.AMP && rootNode.AMP.canonicalUrl;
-    if (!canonicalUrl) {
-      const canonicalTag = user().assert(
-          rootNode.querySelector('link[rel=canonical]'),
-          'AMP files are required to have a <link rel=canonical> tag.');
-      canonicalUrl = parseUrl(canonicalTag.href).href;
-    }
-    const pageViewId = getPageViewId(ampdoc.win);
-    return {url, sourceUrl, canonicalUrl, pageViewId};
-  });
+  return /** @type {!DocumentInfoDef} */ (getServiceForDoc(nodeOrDoc,
+      'documentInfo', ampdoc => {
+        const url = ampdoc.getUrl();
+        const sourceUrl = getSourceUrl(url);
+        const rootNode = ampdoc.getRootNode();
+        let canonicalUrl = rootNode && rootNode.AMP
+            && rootNode.AMP.canonicalUrl;
+        if (!canonicalUrl) {
+          const canonicalTag = user().assert(
+              rootNode.querySelector('link[rel=canonical]'),
+              'AMP files are required to have a <link rel=canonical> tag.');
+          canonicalUrl = parseUrl(canonicalTag.href).href;
+        }
+        const pageViewId = getPageViewId(ampdoc.win);
+        return {url, sourceUrl, canonicalUrl, pageViewId};
+      }));
 }
 
 
diff --git a/src/document-submit.js b/src/document-submit.js
index f28dde673a180..a79954da18db1 100644
--- a/src/document-submit.js
+++ b/src/document-submit.js
@@ -15,7 +15,7 @@
  */
 
 import {startsWith} from './string';
-import {user} from './log';
+import {dev, user} from './log';
 import {assertHttpsUrl, getCorsUrl, SOURCE_ORIGIN_PARAM} from './url';
 import {urls} from './config';
 
@@ -67,7 +67,7 @@ export function onDocumentFormSubmit_(e) {
     action = form.__AMP_INIT_ACTION__;
   }
   user().assert(action, 'form action attribute is required: %s', form);
-  assertHttpsUrl(action, form, 'action');
+  assertHttpsUrl(action, dev().assertElement(form), 'action');
   user().assert(!startsWith(action, urls.cdn),
       'form action should not be on AMP CDN: %s', form);
 
diff --git a/src/error.js b/src/error.js
index f4f72fa2632a9..67d69bf809be9 100644
--- a/src/error.js
+++ b/src/error.js
@@ -42,7 +42,7 @@ let globalExponentialBackoff = function(work) {
  * If the error has a "messageArray" property, that array is logged.
  * This way one gets the native fidelity of the console for things like
  * elements instead of stringification.
- * @param {!Error} error
+ * @param {*} error
  * @param {!Element=} opt_associatedElement
  */
 export function reportError(error, opt_associatedElement) {
@@ -81,7 +81,10 @@ export function reportError(error, opt_associatedElement) {
   if (element && element.dispatchCustomEvent) {
     element.dispatchCustomEvent('amp:error', error.message);
   }
-  reportErrorToServer(undefined, undefined, undefined, undefined, error);
+  // 'call' to make linter happy. And .call to make compiler happy
+  // that expects some @this.
+  reportErrorToServer['call'](undefined, undefined, undefined, undefined,
+      undefined, error);
 }
 
 /**
@@ -97,7 +100,7 @@ export function cancellation() {
  * @param {!Window} win
  */
 export function installErrorReporting(win) {
-  win.onerror = reportErrorToServer;
+  win.onerror = /** @type {!Function} */ (reportErrorToServer);
   win.addEventListener('unhandledrejection', event => {
     reportError(event.reason || new Error('rejected promise ' + event));
   });
@@ -109,7 +112,7 @@ export function installErrorReporting(win) {
  * @param {string|undefined} filename
  * @param {string|undefined} line
  * @param {string|undefined} col
- * @param {!Error|undefined} error
+ * @param {*|undefined} error
  * @this {!Window|undefined}
  */
 function reportErrorToServer(message, filename, line, col, error) {
@@ -134,7 +137,7 @@ function reportErrorToServer(message, filename, line, col, error) {
  * @param {string|undefined} filename
  * @param {string|undefined} line
  * @param {string|undefined} col
- * @param {!Error|undefined} error
+ * @param {*|undefined} error
  * @return {string|undefined} The URL
  * visibleForTesting
  */
@@ -194,8 +197,8 @@ export function getErrorReportUrl(message, filename, line, col, error) {
         '&s=' + encodeURIComponent(error.stack || '');
     error.message += ' _reported_';
   } else {
-    url += '&f=' + encodeURIComponent(filename) +
-        '&l=' + encodeURIComponent(line) +
+    url += '&f=' + encodeURIComponent(filename || '') +
+        '&l=' + encodeURIComponent(line || '') +
         '&c=' + encodeURIComponent(col || '');
   }
   url += '&r=' + encodeURIComponent(self.document.referrer);
diff --git a/src/focus-history.js b/src/focus-history.js
index 77679c14832d0..bb28b14c8b4a1 100644
--- a/src/focus-history.js
+++ b/src/focus-history.js
@@ -16,6 +16,7 @@
 
 import {Observable} from './observable';
 import {timerFor} from './timer';
+import {dev} from './log';
 
 
 /**
@@ -43,7 +44,7 @@ export class FocusHistory {
     /** @private @const {function(!Event)} */
     this.captureFocus_ = e => {
       if (e.target) {
-        this.pushFocus_(e.target);
+        this.pushFocus_(dev().assertElement(e.target));
       }
     };
     /** @private @const {function(!Event)} */
@@ -92,7 +93,7 @@ export class FocusHistory {
 
   /**
    * Returns the element that was focused last.
-   * @return {!Element}
+   * @return {?Element}
    */
   getLast() {
     if (this.history_.length == 0) {
diff --git a/src/history.js b/src/history.js
index dd68e6cbc5417..f79b18f918e8c 100644
--- a/src/history.js
+++ b/src/history.js
@@ -21,8 +21,9 @@ import {getExistingServiceForWindow} from './service';
 /**
  * Returns service implemented in service/history-impl.
  * @param {!Window} window
- * @return {!History}
+ * @return {!./service/history-impl.History}
  */
 export function historyFor(window) {
-  return getExistingServiceForWindow(window, 'history');
+  return /** @type {!./service/history-impl.History} */ (
+      getExistingServiceForWindow(window, 'history'));
 };
diff --git a/src/iframe-helper.js b/src/iframe-helper.js
index 024932a65e76d..447a3ecd04f5c 100644
--- a/src/iframe-helper.js
+++ b/src/iframe-helper.js
@@ -35,7 +35,7 @@ let WindowEventsDef;
 /**
  * Returns a mapping from a URL's origin to an array of windows and their listenFor listeners.
  * @param {!Window} parentWin the window that created the iframe
- * @param {boolean} opt_create create the mapping if it does not exist
+ * @param {boolean=} opt_create create the mapping if it does not exist
  * @return {?Object<string, !Array<!WindowEventsDef>>}
  */
 function getListenFors(parentWin, opt_create) {
@@ -51,7 +51,7 @@ function getListenFors(parentWin, opt_create) {
  * Returns an array of WindowEventsDef that have had any listenFor listeners registered for this sentinel.
  * @param {!Window} parentWin the window that created the iframe
  * @param {string} sentinel the sentinel of the message
- * @param {boolean} opt_create create the array if it does not exist
+ * @param {boolean=} opt_create create the array if it does not exist
  * @return {?Array<!WindowEventsDef>}
  */
 function getListenForSentinel(parentWin, sentinel, opt_create) {
@@ -72,7 +72,7 @@ function getListenForSentinel(parentWin, sentinel, opt_create) {
  * @param {!Window} parentWin the window that created the iframe
  * @param {!Element} iframe the iframe element who's context will trigger the
  *     event
- * @param {string=} opt_is3P set to true if the iframe is 3p.
+ * @param {boolean=} opt_is3P set to true if the iframe is 3p.
  * @return {?Object<string, !Array<function(!Object, !Window, string)>>}
  */
 function getOrCreateListenForEvents(parentWin, iframe, opt_is3P) {
@@ -234,7 +234,7 @@ function registerGlobalListenerIfNeeded(parentWin) {
  *
  * @param {!Element} iframe.
  * @param {string} typeOfMessage.
- * @param {function(!Object, !Window, string)} callback Called when a message of
+ * @param {?function(!Object, !Window, string)} callback Called when a message of
  *     this type arrives for this iframe.
  * @param {boolean=} opt_is3P set to true if the iframe is 3p.
  * @param {boolean=} opt_includingNestedWindows set to true if a messages from
@@ -246,6 +246,7 @@ export function listenFor(
   dev().assert(iframe.src, 'only iframes with src supported');
   dev().assert(!iframe.parentNode, 'cannot register events on an attached ' +
       'iframe. It will cause hair-pulling bugs like #2942');
+  dev().assert(callback);
   const parentWin = iframe.ownerDocument.defaultView;
 
   registerGlobalListenerIfNeeded(parentWin);
@@ -297,7 +298,7 @@ export function listenFor(
  * Returns a promise that resolves when one of given messages has been observed
  * for the first time. And remove listener for all other messages.
  * @param {!Element} iframe
- * @param {string|!Array<string>} typeOfMessage
+ * @param {string|!Array<string>} typeOfMessages
  * @param {boolean=} opt_is3P
  * @return {!Promise<!{data, source, origin}>}
  */
@@ -322,7 +323,7 @@ export function listenForOncePromise(iframe, typeOfMessages, opt_is3P) {
 
 /**
  * Posts a message to the iframe.
- * @param {!Element} element The iframe.
+ * @param {!Element} iframe The iframe.
  * @param {string} type Type of the message.
  * @param {!Object} object Message payload.
  * @param {string} targetOrigin origin of the target.
@@ -351,13 +352,14 @@ export function postMessageToWindows(iframe, targets, type, object, opt_is3P) {
   }
   object.type = type;
   object.sentinel = getSentinel_(iframe, opt_is3P);
+  let payload = object;
   if (opt_is3P) {
     // Serialize ourselves because that is much faster in Chrome.
-    object = 'amp-' + JSON.stringify(object);
+    payload = 'amp-' + JSON.stringify(object);
   }
   for (let i = 0; i < targets.length; i++) {
     const target = targets[i];
-    target.win./*OK*/postMessage(object, target.origin);
+    target.win./*OK*/postMessage(payload, target.origin);
   }
 }
 
@@ -388,7 +390,7 @@ function parseIfNeeded(data) {
           'Is it in a valid JSON format?', e);
     }
   }
-  return data;
+  return /** @type {!Object} */ (data);
 }
 
 
diff --git a/src/intersection-observer.js b/src/intersection-observer.js
index 6a1c84c5a94f3..95ad31ebb3bd9 100644
--- a/src/intersection-observer.js
+++ b/src/intersection-observer.js
@@ -91,13 +91,13 @@ export function getIntersectionChangeEntry(element, owner, viewport) {
       // No intersection.
       layoutRectLtwh(0, 0, 0, 0);
 
-  return {
+  return /** @type {!IntersectionObserverEntry} */ ({
     time: Date.now(),
     rootBounds: DomRectFromLayoutRect(viewport),
     boundingClientRect: DomRectFromLayoutRect(element),
     intersectionRect: DomRectFromLayoutRect(intersectionRect),
     intersectionRatio: intersectionRatio(intersectionRect, element),
-  };
+  });
 }
 
 /**
@@ -140,7 +140,7 @@ export class IntersectionObserver {
     /** @private {!Array<!IntersectionObserverEntry>} */
     this.pendingChanges_ = [];
 
-    /** @private {number} */
+    /** @private {number|string} */
     this.flushTimeout_ = 0;
 
     /** @private @const {function()} */
@@ -158,6 +158,9 @@ export class IntersectionObserver {
         // Each time someone subscribes we make sure that they
         // get an update.
         () => this.startSendingIntersectionChanges_());
+
+    /** @private {?Function} */
+    this.unlistenViewportChanges_ = null;
   }
 
   fire() {
diff --git a/src/json.js b/src/json.js
index 026a295236a58..64a5a952e80c2 100644
--- a/src/json.js
+++ b/src/json.js
@@ -112,7 +112,7 @@ export function getValueForExpr(obj, expr) {
  */
 export function tryParseJson(json, opt_onFailed) {
   try {
-    return JSON.parse(json);
+    return JSON.parse(/** @type {string} */ (json));
   } catch (e) {
     if (opt_onFailed) {
       opt_onFailed(e);
diff --git a/src/layout-rect.js b/src/layout-rect.js
index b913aafb77af0..4520e86e0f70b 100644
--- a/src/layout-rect.js
+++ b/src/layout-rect.js
@@ -59,10 +59,10 @@ export function layoutRectLtwh(left, top, width, height) {
  * @return {!LayoutRectDef}
  */
 export function layoutRectFromDomRect(rect) {
-  return layoutRectLtwh(rect.left, rect.top, rect.width, rect.height);
+  return layoutRectLtwh(Number(rect.left), Number(rect.top),
+      Number(rect.width), Number(rect.height));
 }
 
-
 /**
  * Returns true if the specified two rects overlap by a single pixel.
  * @param {!LayoutRectDef} r1
diff --git a/src/layout.js b/src/layout.js
index a224f0cdb0098..0353c2462be7b 100644
--- a/src/layout.js
+++ b/src/layout.js
@@ -167,14 +167,14 @@ export function parseLength(s) {
 
 /**
  * Asserts that the supplied value is a non-percent CSS Length value.
- * @param {!LengthDef|string} length
+ * @param {!LengthDef|string|null|undefined} length
  * @return {!LengthDef}
  */
 export function assertLength(length) {
   user().assert(
       /^\d+(\.\d+)?(px|em|rem|vh|vw|vmin|vmax|cm|mm|q|in|pc|pt)$/.test(length),
       'Invalid length value: %s', length);
-  return length;
+  return /** @type {!LengthDef} */ (length);
 }
 
 
@@ -195,11 +195,12 @@ export function assertLengthOrPercent(length) {
 
 /**
  * Returns units from the CSS length value.
- * @param {!LengthDef} length
+ * @param {!LengthDef|string|null|undefined} length
  * @return {string}
  */
 export function getLengthUnits(length) {
   assertLength(length);
+  dev().assertString(length);
   const m = user().assert(length.match(/[a-z]+/i),
       'Failed to read units from %s', length);
   return m[0];
@@ -208,7 +209,7 @@ export function getLengthUnits(length) {
 
 /**
  * Returns the numeric value of a CSS length value.
- * @param {!LengthDef|string} length
+ * @param {!LengthDef|string|null|undefined} length
  * @return {number|undefined}
  */
 export function getLengthNumeral(length) {
@@ -221,7 +222,7 @@ export function getLengthNumeral(length) {
  * Determines whether the tagName is a known element that has natural dimensions
  * in our runtime or the browser.
  * @param {string} tagName The element tag name.
- * @return {DimensionsDef}
+ * @return {boolean}
  */
 export function hasNaturalDimensions(tagName) {
   tagName = tagName.toUpperCase();
@@ -255,7 +256,7 @@ export function getNaturalDimensions(element) {
     };
     doc.body.removeChild(temp);
   }
-  return naturalDimensions_[tagName];
+  return /** @type {DimensionsDef} */ (naturalDimensions_[tagName]);
 }
 
 
diff --git a/src/log.js b/src/log.js
index 9978094af7e32..deddf0ec77ea1 100644
--- a/src/log.js
+++ b/src/log.js
@@ -268,6 +268,23 @@ export class Log {
     return /** @type {!Element} */ (shouldBeElement);
   }
 
+  /**
+   * Throws an error if the first argument isn't a string.
+   *
+   * Otherwise see `assert` for usage
+   *
+   * @param {*} shouldBeString
+   * @param {string=} opt_message The assertion message
+   * @return {string} The value of shouldBeTrueish.
+   * @template T
+   */
+  /*eslint "google-camelcase/google-camelcase": 2*/
+  assertString(shouldBeString, opt_message) {
+    this.assert(typeof shouldBeString == 'string',
+        (opt_message || 'String expected') + ': %s', shouldBeString);
+    return /** @type {string} */ (shouldBeString);
+  }
+
   /**
    * Asserts and returns the enum value. If the enum doesn't contain such a value,
    * the error is thrown.
diff --git a/src/pass.js b/src/pass.js
index b7092d4c6ec15..33422952776e8 100644
--- a/src/pass.js
+++ b/src/pass.js
@@ -37,7 +37,7 @@ export class Pass {
     /** @private @const {function()} */
     this.handler_ = handler;
 
-    /** @private @const {number|string} */
+    /** @private @const {number} */
     this.defaultDelay_ = opt_defaultDelay || 0;
 
     /** @private {number|string} */
diff --git a/src/platform.js b/src/platform.js
index 5a11355864410..46c08a1fae4f0 100644
--- a/src/platform.js
+++ b/src/platform.js
@@ -28,7 +28,7 @@ export class Platform {
    */
   constructor(win) {
     /** @const {!Navigator} */
-    this.navigator = win.navigator;
+    this.navigator = /** @type {!Navigator} */ (win.navigator);
   }
 
   /**
diff --git a/src/preconnect.js b/src/preconnect.js
index 32ea40433b881..63f419411e5b5 100644
--- a/src/preconnect.js
+++ b/src/preconnect.js
@@ -25,6 +25,7 @@ import {parseUrl} from './url';
 import {timerFor} from './timer';
 import {platformFor} from './platform';
 import {viewerFor} from './viewer';
+import {dev} from './log';
 
 const ACTIVE_CONNECTION_TIMEOUT_MS = 180 * 1000;
 const PRECONNECT_TIMEOUT_MS = 10 * 1000;
@@ -39,7 +40,7 @@ export class Preconnect {
     this.document_ = win.document;
 
     /** @private @const {!Element} */
-    this.head_ = win.document.head;
+    this.head_ = dev().assertElement(win.document.head);
     /**
      * Origin we've preconnected to and when that connection
      * expires as a timestamp in MS.
@@ -60,7 +61,10 @@ export class Preconnect {
      * Detect support for the given resource hints.
      * Unfortunately not all browsers support this, so this can only
      * be used as an affirmative signal.
-     * @private @const {{preload: boolean, preconnect: boolean}}
+     * @private @const {{
+     *   preload: (boolean|undefined),
+     *   preconnect: (boolean|undefined)
+     * }}
      */
     this.features_ = this.detectFeatures_();
 
@@ -191,11 +195,14 @@ export class Preconnect {
   /**
    * Detect related features if feature detection is supported by the
    * browser. Even if this fails, the browser may support the feature.
-   * @return {{preload: boolean, preconnect: boolean}}
+   * @return {{
+   *   preload: (boolean|undefined),
+   *   preconnect: (boolean|undefined)
+   * }}
    * @private
    */
   detectFeatures_() {
-    const tokenList = this.document_.createElement('link').relList;
+    const tokenList = this.document_.createElement('link')['relList'];
     if (!tokenList || !tokenList.supports) {
       return {};
     }
diff --git a/src/pull-to-refresh.js b/src/pull-to-refresh.js
index ea4695366e936..3b828a356705d 100644
--- a/src/pull-to-refresh.js
+++ b/src/pull-to-refresh.js
@@ -83,7 +83,7 @@ export class PullToRefreshBlocker {
     // already tracking this touch and for non-single-touch events.
     if (this.tracking_ ||
           !(event.touches && event.touches.length == 1) ||
-          this.viewport_.getTop() > 0) {
+          this.viewport_.getScrollTop() > 0) {
       return;
     }
 
diff --git a/src/runtime.js b/src/runtime.js
index 3d7ec2bbab156..f2eade12c7fc1 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -163,10 +163,7 @@ function adoptShared(global, opts, callback) {
 
   /**
    * Registers an extended element and installs its styles.
-   * @param {string} name
-   * @param {!Function} implementationClass
-   * @param {string=} opt_css Optional CSS to install with the component.
-   *     Typically imported from generated CSS-in-JS file for each component.
+   * @const
    */
   global.AMP.registerElement = opts.registerElement.bind(null,
       global, extensions);
@@ -182,9 +179,7 @@ function adoptShared(global, opts, callback) {
 
   /**
    * Registers an ampdoc service.
-   * @param {string} name
-   * @param {function(new:Object, !./service/ampdoc-impl.AmpDoc)=} opt_ctor
-   * @param {function(!./service/ampdoc-impl.AmpDoc):!Object=} opt_factory
+   * @const
    */
   global.AMP.registerServiceForDoc = opts.registerServiceForDoc.bind(null,
       global, extensions);
@@ -358,7 +353,7 @@ function prepareAndRegisterElementShadowMode(global, extensions,
   registerElementClass(global, name, implementationClass, opt_css);
   if (opt_css) {
     addShadowRootFactoryToExtension(extensions, shadowRoot => {
-      installStylesForShadowRoot(shadowRoot, opt_css,
+      installStylesForShadowRoot(shadowRoot, dev().assertString(opt_css),
           /* isRuntimeCss */ false, name);
     });
   }
@@ -506,12 +501,13 @@ function mergeShadowHead(global, extensions, shadowRoot, doc) {
   const extensionIds = [];
   if (doc.head) {
     const parentLinks = {};
-    childElementsByTag(global.document.head, 'link').forEach(link => {
-      const href = link.getAttribute('href');
-      if (href) {
-        parentLinks[href] = true;
-      }
-    });
+    childElementsByTag(dev().assertElement(global.document.head), 'link')
+        .forEach(link => {
+          const href = link.getAttribute('href');
+          if (href) {
+            parentLinks[href] = true;
+          }
+        });
 
     for (let n = doc.head.firstElementChild; n; n = n.nextElementSibling) {
       const tagName = n.tagName;
diff --git a/src/service/action-impl.js b/src/service/action-impl.js
index a6f4d72a934d5..e1eeee9a4bf64 100644
--- a/src/service/action-impl.js
+++ b/src/service/action-impl.js
@@ -115,12 +115,12 @@ export class ActionService {
       // fast-click.
       this.ampdoc.getRootNode().addEventListener('click', event => {
         if (!event.defaultPrevented) {
-          this.trigger(event.target, 'tap', event);
+          this.trigger(dev().assertElement(event.target), 'tap', event);
         }
       });
     } else if (name == 'submit') {
       this.ampdoc.getRootNode().addEventListener('submit', event => {
-        this.trigger(event.target, 'submit', event);
+        this.trigger(dev().assertElement(event.target), 'submit', event);
       });
     }
   }
@@ -196,7 +196,7 @@ export class ActionService {
   /**
    * @param {!Element} source
    * @param {string} actionEventType
-   * @param {!Event} event
+   * @param {?Event} event
    * @private
    */
   action_(source, actionEventType, event) {
@@ -442,7 +442,7 @@ function assertActionForParser(s, context, condition, opt_message) {
  * @param {!{type: TokenType, value: *}} tok
  * @param {TokenType} type
  * @param {*=} opt_value
- * @return {!{type: string, value: *}}
+ * @return {!{type: TokenType, value: *}}
  * @private
  */
 function assertTokenForParser(s, context, tok, type, opt_value) {
diff --git a/src/service/ampdoc-impl.js b/src/service/ampdoc-impl.js
index 73e7a56597ad6..ada70b1a81dba 100644
--- a/src/service/ampdoc-impl.js
+++ b/src/service/ampdoc-impl.js
@@ -78,7 +78,7 @@ export class AmpDocService {
     /** @const {!Window} */
     this.win = win;
 
-    /** @private @const {?AmpDoc} */
+    /** @private {?AmpDoc} */
     this.singleDoc_ = null;
     if (isSingleDoc) {
       this.singleDoc_ = new AmpDocSingle(win);
@@ -100,7 +100,7 @@ export class AmpDocService {
    * instance is always returned. Otherwise, this method locates the `AmpDoc`
    * that contains the specified node and, if necessary, initializes it.
    *
-   * @param {!Node} node
+   * @param {!Node=} node
    * @return {!AmpDoc}
    */
   getAmpDoc(node) {
@@ -108,7 +108,7 @@ export class AmpDocService {
     if (this.singleDoc_) {
       return this.singleDoc_;
     }
-
+    dev().assert(node);
     // Otherwise discover and possibly create the ampdoc.
     let n = node;
     while (n) {
@@ -140,7 +140,7 @@ export class AmpDocService {
    * Creates and installs the ampdoc for the shadow root.
    * @param {string} url
    * @param {!ShadowRoot} shadowRoot
-   * @return {!AmpDoc}
+   * @return {!AmpDocShadow}
    * @private
    */
   installShadowDoc_(url, shadowRoot) {
@@ -175,7 +175,7 @@ export class AmpDoc {
    * @return {boolean}
    */
   isSingleDoc() {
-    return dev().assert(null, 'not implemented');
+    return /** @type {?} */ (dev().assert(null, 'not implemented'));
   }
 
   /**
@@ -195,7 +195,7 @@ export class AmpDoc {
    * @return {!Document|!ShadowRoot}
    */
   getRootNode() {
-    return dev().assert(null, 'not implemented');
+    return /** @type {?} */ (dev().assert(null, 'not implemented'));
   }
 
   /**
@@ -204,7 +204,7 @@ export class AmpDoc {
    * @return {boolean}
    */
   isBodyAvailable() {
-    return dev().assert(false, 'not implemented');
+    return /** @type {?} */ (dev().assert(false, 'not implemented'));
   }
 
   /**
@@ -215,7 +215,7 @@ export class AmpDoc {
    * @return {!Element}
    */
   getBody() {
-    return dev().assert(null, 'not implemented');
+    return dev().assertElement(null, 'not implemented');
   }
 
   /**
@@ -224,7 +224,7 @@ export class AmpDoc {
    * @return {!Promise<!Element>}
    */
   whenBodyAvailable() {
-    return dev().assert(null, 'not implemented');
+    return /** @type {?} */ (dev().assert(null, 'not implemented'));
   }
 
   /**
@@ -235,7 +235,7 @@ export class AmpDoc {
    * @return {boolean}
    */
   isReady() {
-    return dev().assert(null, 'not implemented');;
+    return /** @type {?} */ (dev().assert(null, 'not implemented'));
   }
 
   /**
@@ -244,7 +244,7 @@ export class AmpDoc {
    * @return {!Promise}
    */
   whenReady() {
-    return dev().assert(null, 'not implemented');
+    return /** @type {?} */ (dev().assert(null, 'not implemented'));
   }
 
   /**
@@ -252,7 +252,7 @@ export class AmpDoc {
    * @return {string}
    */
   getUrl() {
-    return dev().assert(null, 'not implemented');
+    return dev().assertString(null, 'not implemented');
   }
 
   /**
@@ -314,7 +314,7 @@ export class AmpDocSingle extends AmpDoc {
 
   /** @override */
   getBody() {
-    return dev().assert(this.win.document.body, 'body not available');
+    return dev().assertElement(this.win.document.body, 'body not available');
   }
 
   /** @override */
@@ -397,7 +397,7 @@ export class AmpDocShadow extends AmpDoc {
 
   /** @override */
   getBody() {
-    return dev().assert(this.body_, 'body not available');
+    return dev().assertElement(this.body_, 'body not available');
   }
 
   /**
@@ -445,7 +445,7 @@ export class AmpDocShadow extends AmpDoc {
  * @return {!AmpDocService}
  */
 export function installDocService(win, isSingleDoc) {
-  return getService(win, 'ampdoc', () => {
+  return /** @type {!AmpDocService} */ (getService(win, 'ampdoc', () => {
     return new AmpDocService(win, isSingleDoc);
-  });
+  }));
 };
diff --git a/src/service/extensions-impl.js b/src/service/extensions-impl.js
index 04894fcd8dce4..8d434a6a1c732 100644
--- a/src/service/extensions-impl.js
+++ b/src/service/extensions-impl.js
@@ -30,7 +30,7 @@ const UNKNOWN_EXTENSION = '_UNKNOWN_';
  * Currently only limitted to elements.
  *
  * @typedef {{
- *   elements: !Array<!{implementationClass:
+ *   elements: !Object<string, !{implementationClass:
  *       function(new:../base-element.BaseElement, !Element)}>,
  * }}
  */
@@ -286,7 +286,7 @@ export class Extensions {
       promises.push(this.waitFor_(holder).then(() => {
         holder.shadowRootFactories.forEach(factory => {
           try {
-            factory(ampdoc.getRootNode());
+            factory(/** @type {!ShadowRoot} */ (ampdoc.getRootNode()));
           } catch (e) {
             rethrowAsync('ShadowRoot factory failed: ', e, extensionId);
           }
@@ -318,7 +318,7 @@ export class Extensions {
       promises.push(this.waitFor_(holder).then(() => {
         holder.shadowRootFactories.forEach(factory => {
           try {
-            factory(shadowRoot);
+            factory(/** @type {!ShadowRoot} */ (shadowRoot));
           } catch (e) {
             rethrowAsync('ShadowRoot factory failed: ', e, extensionId);
           }
@@ -340,7 +340,7 @@ export class Extensions {
       const extension = {
         elements: {},
       };
-      holder = {
+      holder = /** @type {ExtensionHolderDef} */ ({
         extension,
         docFactories: [],
         shadowRootFactories: [],
@@ -350,7 +350,7 @@ export class Extensions {
         loaded: undefined,
         error: undefined,
         scriptPresent: undefined,
-      };
+      });
       this.extensions_[extensionId] = holder;
     }
     return holder;
@@ -397,7 +397,6 @@ export class Extensions {
    * Ensures that the script has already been injected in the page.
    * @param {string} extensionId
    * @param {!ExtensionHolderDef} holder
-   * @return {boolean}
    * @private
    */
   insertExtensionScriptIfNeeded_(extensionId, holder) {
@@ -431,7 +430,7 @@ export class Extensions {
   /**
    * Create the missing amp extension HTML script element.
    * @param {string} extensionId
-   * @return {!HTMLScriptElement} Script object
+   * @return {!Element} Script object
    * @private
    */
   createExtensionScript_(extensionId) {
diff --git a/src/service/fixed-layer.js b/src/service/fixed-layer.js
index cc013a85186ed..3ea7823ac0732 100644
--- a/src/service/fixed-layer.js
+++ b/src/service/fixed-layer.js
@@ -168,10 +168,10 @@ export class FixedLayer {
    * @param {!Element} element
    */
   removeElement(element) {
-    this.removeFixedElement_(element);
-    if (this.fixedLayer_) {
+    const fe = this.removeFixedElement_(element);
+    if (fe && this.fixedLayer_) {
       this.vsync_.mutate(() => {
-        this.returnFromFixedLayer_(element);
+        this.returnFromFixedLayer_(/** @type {FixedElementDef} */ (fe));
       });
     }
   }
@@ -413,6 +413,7 @@ export class FixedLayer {
    * Removes element from the fixed layer.
    *
    * @param {!Element} element
+   * @return {FixedElementDef|undefined} [description]
    * @private
    */
   removeFixedElement_(element) {
@@ -421,10 +422,12 @@ export class FixedLayer {
         this.vsync_.mutate(() => {
           element.style.top = '';
         });
+        const fe = this.fixedElements_[i];
         this.fixedElements_.splice(i, 1);
-        break;
+        return fe;
       }
     }
+    return undefined;
   }
 
   /** @private */
@@ -642,10 +645,10 @@ export class FixedLayer {
  *   id: string,
  *   selectors: !Array,
  *   element: !Element,
- *   placeholder: ?Element,
- *   fixedNow: boolean,
- *   top: string,
- *   transform: string,
+ *   placeholder: (?Element|undefined),
+ *   fixedNow: (boolean|undefined),
+ *   top: (string|undefined),
+ *   transform: (string|undefined),
  * }}
  */
 let FixedElementDef;
diff --git a/src/service/history-impl.js b/src/service/history-impl.js
index 00bcd809ccdd2..4ff9874739d02 100644
--- a/src/service/history-impl.js
+++ b/src/service/history-impl.js
@@ -314,10 +314,10 @@ export class HistoryBindingNatural_ {
       };
     }
 
-    /** @private @const {function(*, string=, string=)} */
+    /** @private @const {!Function} */
     this.pushState_ = pushState;
 
-    /** @private @const {function(*, string=, string=)} */
+    /** @private @const {!Function} */
     this.replaceState_ = replaceState;
 
     try {
@@ -503,9 +503,9 @@ export class HistoryBindingNatural_ {
   }
 
   /**
-   * @param {*} state
-   * @param {string|undefined} title
-   * @param {string|undefined} url
+   * @param {*=} state
+   * @param {(string|undefined)=} title
+   * @param {(string|undefined)=} url
    * @private
    */
   historyPushState_(state, title, url) {
@@ -525,9 +525,9 @@ export class HistoryBindingNatural_ {
   }
 
   /**
-   * @param {*} state
-   * @param {string|undefined} title
-   * @param {string|undefined} url
+   * @param {*=} state
+   * @param {(string|undefined)=} title
+   * @param {(string|undefined)=} url
    * @private
    */
   historyReplaceState_(state, title, url) {
diff --git a/src/service/performance-impl.js b/src/service/performance-impl.js
index 13fb0adb97e36..1f9a99317084f 100644
--- a/src/service/performance-impl.js
+++ b/src/service/performance-impl.js
@@ -213,7 +213,7 @@ export class Performance {
   /**
    * Forward an object to be appended as search params to the external
    * intstrumentation library.
-   * @param {!JSONType} params
+   * @param {!Object} params
    * @private
    */
   setFlushParams_(params) {
diff --git a/src/service/resource.js b/src/service/resource.js
index 2c90475f007fa..5a6d168852263 100644
--- a/src/service/resource.js
+++ b/src/service/resource.js
@@ -74,8 +74,9 @@ export class Resource {
    * @return {!Resource}
    */
   static forElement(element) {
-    return dev().assert(Resource.forElementOptional(element),
-        'Missing resource prop on %s', element);
+    return /** @type {!Resource} */ (
+        dev().assert(Resource.forElementOptional(element),
+            'Missing resource prop on %s', element));
   }
 
   /**
@@ -120,7 +121,7 @@ export class Resource {
     /** @private {boolean} */
     this.blacklisted_ = false;
 
-    /** @const {!AmpElement|undefined|null} */
+    /** @private {!AmpElement|undefined|null} */
     this.owner_ = undefined;
 
     /** @private {!ResourceState} */
@@ -157,9 +158,11 @@ export class Resource {
     /** @private {boolean} */
     this.loadedOnce_ = false;
 
+    /** @private {?Function} */
+    this.loadPromiseResolve_ = null;
+
     /** @private @const {!Promise} */
     this.loadPromise_ = new Promise(resolve => {
-      /** @const  */
       this.loadPromiseResolve_ = resolve;
     }).then(() => {
       this.loadedOnce_ = true;
diff --git a/src/service/resources-impl.js b/src/service/resources-impl.js
index 6bf48c0d18a98..5e1cabba22f27 100644
--- a/src/service/resources-impl.js
+++ b/src/service/resources-impl.js
@@ -54,7 +54,7 @@ const FOUR_FRAME_DELAY_ = 70;
  *   newHeight: (number|undefined),
  *   newWidth: (number|undefined),
  *   force: boolean,
- *   callback: (function()|undefined)
+ *   callback: (function(boolean)|undefined)
  * }}
  */
 let ChangeSizeRequestDef;
@@ -301,7 +301,6 @@ export class Resources {
    * Element. If no Resource is found, the exception is thrown.
    * @param {!AmpElement} element
    * @return {!Resource}
-   * @package
    */
   getResourceForElement(element) {
     return Resource.forElement(element);
@@ -330,7 +329,6 @@ export class Resources {
    * Signals that an element has been added to the DOM. Resources manager
    * will start tracking it from this point on.
    * @param {!AmpElement} element
-   * @package
    */
   add(element) {
     const resource = new Resource((++this.resourceIdCounter_), element, this);
@@ -410,7 +408,6 @@ export class Resources {
    * Signals that an element has been removed to the DOM. Resources manager
    * will stop tracking it from this point on.
    * @param {!AmpElement} element
-   * @package
    */
   remove(element) {
     const resource = Resource.forElementOptional(element);
@@ -430,7 +427,6 @@ export class Resources {
    * Signals that an element has been upgraded to the DOM. Resources manager
    * will perform build and enable layout/viewport signals for this element.
    * @param {!AmpElement} element
-   * @package
    */
   upgraded(element) {
     const resource = Resource.forElement(element);
@@ -1110,13 +1106,13 @@ export class Resources {
         const reschedule = this.reschedule_.bind(this, task);
         executing.promise.then(reschedule, reschedule);
       } else {
-        task.promise = task.callback(visibility);
+        task.promise = task.callback(visibility == 'visible');
         task.startTime = now;
         dev().fine(TAG_, 'exec:', task.id, 'at', task.startTime);
         this.exec_.enqueue(task);
         task.promise.then(this.taskComplete_.bind(this, task, true),
             this.taskComplete_.bind(this, task, false))
-            .catch(reportError);
+            .catch(/** @type {function (*)} */ (reportError));
       }
 
       task = this.queue_.peek(this.boundTaskScorer_);
@@ -1255,7 +1251,7 @@ export class Resources {
    * @param {number|undefined} newHeight
    * @param {number|undefined} newWidth
    * @param {boolean} force
-   * @param {function()=} opt_callback A callback function
+   * @param {function(boolean)=} opt_callback A callback function
    * @private
    */
   scheduleChangeSize_(resource, newHeight, newWidth, force,
@@ -1383,7 +1379,7 @@ export class Resources {
    * @param {string} localId
    * @param {number} priorityOffset
    * @param {number} parentPriority
-   * @param {function():!Promise} callback
+   * @param {function(boolean):!Promise} callback
    * @private
    */
   schedule_(resource, localId, priorityOffset, parentPriority, callback) {
@@ -1477,7 +1473,7 @@ export class Resources {
 
   /**
    * Calls iterator on each sub-resource
-   * @param {function(!Resource, number)} iterator
+   * @param {!FiniteStateMachine<!VisibilityState>} vsm
    */
   setupVisibilityStateMachine_(vsm) {
     const prerender = VisibilityState.PRERENDER;
@@ -1565,8 +1561,9 @@ export class Resources {
 
   /**
    * Cleanup task queues from tasks for elements that has been unloaded.
-   * @param resource
-   * @param opt_removePending Whether to remove from pending build resources.
+   * @param {Resource} resource
+   * @param {boolean=} opt_removePending Whether to remove from pending
+   *     build resources.
    * @private
    */
   cleanupTasks_(resource, opt_removePending) {
@@ -1603,7 +1600,8 @@ export class Resources {
  * @return {!Array<!Element>}
  */
 function elements_(elements) {
-  return isArray(elements) ? elements : [elements];
+  return /** @type {!Array<!Element>} */ (
+      isArray(elements) ? elements : [elements]);
 }
 
 
diff --git a/src/service/task-queue.js b/src/service/task-queue.js
index ceb01caf5047a..bfe0aee756154 100644
--- a/src/service/task-queue.js
+++ b/src/service/task-queue.js
@@ -26,7 +26,7 @@ import {dev} from '../log';
  *   callback: function(boolean),
  *   scheduleTime: time,
  *   startTime: time,
- *   promise: (!Promise|undefined)
+ *   promise: (?Promise|undefined)
  * }}
  */
 export let TaskDef;
diff --git a/src/service/url-replacements-impl.js b/src/service/url-replacements-impl.js
index 852a8b243d35c..a8970f7e51d2c 100644
--- a/src/service/url-replacements-impl.js
+++ b/src/service/url-replacements-impl.js
@@ -53,13 +53,16 @@ export class UrlReplacements {
     /** @private @const {!Object<string, function(*, *):*>} */
     this.replacements_ = this.win_.Object.create(null);
 
-    /** @private @const {function():!Promise<?AccessService>} */
+    /** @private @const {function(!Window):!Promise<?AccessService>} */
     this.getAccessService_ = accessServiceForOrNull;
 
-    /** @private @const {!Promise<?Object<string, ?string>>} */
+    /** @private @const {!Promise<?Object<string>>} */
     this.variants_ = variantForOrNull(win);
 
-    /** @private @const {!Promise<?Object<string, string>>} */
+    /**
+     * @private @const {
+     *   !Promise<(?{incomingFragment: string, outgoingFragment: string})>}
+     */
     this.shareTrackingFragments_ = shareTrackingForOrNull(win);
 
     /** @private {boolean} */
@@ -166,7 +169,8 @@ export class UrlReplacements {
     });
 
     this.set_('CLIENT_ID', (scope, opt_userNotificationId) => {
-      user().assert(scope, 'The first argument to CLIENT_ID, the fallback c' +
+      user().assertString(scope,
+          'The first argument to CLIENT_ID, the fallback c' +
           /*OK*/'ookie name, is required');
       let consent = Promise.resolve();
 
@@ -179,7 +183,7 @@ export class UrlReplacements {
       }
       return cidFor(this.win_).then(cid => {
         return cid.get({
-          scope,
+          scope: dev().assertString(scope),
           createCookieIfNotPresent: true,
         }, consent);
       });
@@ -426,7 +430,7 @@ export class UrlReplacements {
    * @template T
    */
   getAccessValue_(getter, expr) {
-    return this.getAccessService_().then(accessService => {
+    return this.getAccessService_(this.win_).then(accessService => {
       if (!accessService) {
         // Access service is not installed.
         user().error(TAG, 'Access service is not installed to access: ', expr);
diff --git a/src/service/viewer-impl.js b/src/service/viewer-impl.js
index 06e5b4a0f8691..d23804d4ed741 100644
--- a/src/service/viewer-impl.js
+++ b/src/service/viewer-impl.js
@@ -314,7 +314,6 @@ export class Viewer {
       } else {
         // Race to resolve with a timer.
         timerFor(this.win).delay(() => resolve(''), VIEWER_ORIGIN_TIMEOUT_);
-        /** @private @const {!function(string)|undefined} */
         this.viewerOriginResolver_ = resolve;
       }
     });
@@ -735,7 +734,11 @@ export class Viewer {
 
   /**
    * Adds a "viewport" event listener for viewer events.
-   * @param {function()} handler
+   * @param {function({
+   *   paddingTop: number,
+   *   duration: (number|undefined),
+   *   curve: (string|undefined)
+   * })} handler
    * @return {!UnlistenDef}
    */
   onViewportEvent(handler) {
@@ -863,7 +866,7 @@ export class Viewer {
 
   /**
    * Triggers "tick" event for the viewer.
-   * @param {!JSONType} message
+   * @param {!Object} message
    */
   tick(message) {
     this.sendMessageUnreliable_('tick', message, false);
@@ -878,7 +881,7 @@ export class Viewer {
 
   /**
    * Triggers "setFlushParams" event for the viewer.
-   * @param {!JSONType} message
+   * @param {!Object} message
    */
   setFlushParams(message) {
     this.sendMessageUnreliable_('setFlushParams', message, false);
@@ -886,7 +889,7 @@ export class Viewer {
 
   /**
    * Triggers "prerenderComplete" event for the viewer.
-   * @param {!JSONType} message
+   * @param {!Object} message
    */
   prerenderComplete(message) {
     this.sendMessageUnreliable_('prerenderComplete', message, false);
diff --git a/src/service/viewport-impl.js b/src/service/viewport-impl.js
index cc98e50286722..c42b125137da0 100644
--- a/src/service/viewport-impl.js
+++ b/src/service/viewport-impl.js
@@ -669,8 +669,8 @@ export class ViewportBindingDef {
   /**
    * Updates binding with the new padding.
    * @param {number} unusedPaddingTop
-   * @param {boolean|undefined} unusedOptUpdateScrollPos
-   * @param {number|undefined} unusedOptLastPaddingTop
+   * @param {(boolean|undefined)=} unusedOptUpdateScrollPos
+   * @param {(number|undefined)=} unusedOptLastPaddingTop
    */
   updatePaddingTop(unusedPaddingTop, unusedOptUpdateScrollPos,
       unusedOptLastPaddingTop) {}
diff --git a/src/share-tracking-service.js b/src/share-tracking-service.js
index 8f08dcebfdade..71254501d7a02 100644
--- a/src/share-tracking-service.js
+++ b/src/share-tracking-service.js
@@ -20,10 +20,11 @@ import {getElementServiceIfAvailable} from './element-service';
  * Returns a promise for the share tracking fragments or a promise for null
  * if it is not available on the current page.
  * @param {!Window} win
- * @return {!Promise<?Object<string, string>>}
+ * @return {!Promise<?{incomingFragment: string, outgoingFragment: string}>}
  */
 export function shareTrackingForOrNull(win) {
-  return /** @type {!Promise<?Object<string, string>>} */ (
+  return (/** @type {
+    !Promise<?{incomingFragment: string, outgoingFragment: string}>} */ (
       getElementServiceIfAvailable(win, 'share-tracking',
-          'amp-share-tracking'));
+          'amp-share-tracking')));
 }
diff --git a/src/style.js b/src/style.js
index 5ab1e09aa40c9..e33d05341180f 100644
--- a/src/style.js
+++ b/src/style.js
@@ -87,7 +87,7 @@ export function getVendorJsPropertyName(style, camelCase, opt_bypassCache) {
 
 /**
  * Sets the CSS style of the specified element with optional units, e.g. "px".
- * @param {!Element} element
+ * @param {Element} element
  * @param {string} property
  * @param {*} value
  * @param {string=} opt_units
diff --git a/src/url.js b/src/url.js
index 49b8efb501c7e..11e237e6d6aad 100644
--- a/src/url.js
+++ b/src/url.js
@@ -240,7 +240,7 @@ export function assertAbsoluteHttpOrHttpsUrl(urlString) {
  * Parses the query string of an URL. This method returns a simple key/value
  * map. If there are duplicate keys the latest value is returned.
  * @param {string} queryString
- * @return {!Object<string, string>}
+ * @return {!Object<string>}
  */
 export function parseQueryString(queryString) {
   const params = Object.create(null);
diff --git a/src/variant-service.js b/src/variant-service.js
index d9bb444349bac..e0b3566c447e1 100644
--- a/src/variant-service.js
+++ b/src/variant-service.js
@@ -20,9 +20,9 @@ import {getElementServiceIfAvailable} from './element-service';
  * Returns a promise for the experiment variants or a promise for null if it is
  * not available on the current page.
  * @param {!Window} win
- * @return {!Promise<?Object<string, string>>}
+ * @return {!Promise<?Object<string>>}
  */
 export function variantForOrNull(win) {
-  return /** @type {!Promise<?Object<string, string>>} */ (
+  return /** @type {!Promise<?Object<string>>} */ (
       getElementServiceIfAvailable(win, 'variant', 'amp-experiment'));
 }
diff --git a/test/functional/test-3p-frame.js b/test/functional/test-3p-frame.js
index 85e00f2aa9034..47917a7a0882a 100644
--- a/test/functional/test-3p-frame.js
+++ b/test/functional/test-3p-frame.js
@@ -297,6 +297,8 @@ describe('3p-frame', () => {
 
     const div = document.createElement('div');
     div.setAttribute('type', '_ping_');
+    div.setAttribute('width', 100);
+    div.setAttribute('height', 200);
     div.getIntersectionChangeEntry = function() {
       return {
         left: 0,
diff --git a/test/functional/test-ampdoc.js b/test/functional/test-ampdoc.js
index de00f588b5607..2795f82b60594 100644
--- a/test/functional/test-ampdoc.js
+++ b/test/functional/test-ampdoc.js
@@ -242,7 +242,7 @@ describe('AmpDocSingle', () => {
     const bodyPromise = ampdoc.whenBodyAvailable();
     const readyPromise = ampdoc.whenReady();
 
-    doc.body = {};
+    doc.body = {nodeType: 1};
     bodyCallback();
     ready = true;
     readyCallback();
@@ -317,7 +317,7 @@ describe('AmpDocShadow', () => {
 
     // Set body.
     const bodyPromise = ampdoc.whenBodyAvailable();
-    const body = {};
+    const body = {nodeType: 1};
     shadowDocHasBody(ampdoc, body);
     expect(ampdoc.isBodyAvailable()).to.be.true;
     expect(ampdoc.getBody()).to.equal(body);
@@ -330,7 +330,7 @@ describe('AmpDocShadow', () => {
   });
 
   it('should only allow one body update', () => {
-    const body = {};
+    const body = {nodeType: 1};
     shadowDocHasBody(ampdoc, body);
     expect(() => {
       shadowDocHasBody(ampdoc, body);
diff --git a/test/functional/test-pull-to-refresh.js b/test/functional/test-pull-to-refresh.js
index 844cd37aa5f57..c40140a03434b 100644
--- a/test/functional/test-pull-to-refresh.js
+++ b/test/functional/test-pull-to-refresh.js
@@ -41,7 +41,7 @@ describe('PullToRefreshBlocker', () => {
     };
 
     const viewportApi = {
-      getTop: () => 0,
+      getScrollTop: () => 0,
     };
     viewportMock = sandbox.mock(viewportApi);
 
@@ -93,7 +93,7 @@ describe('PullToRefreshBlocker', () => {
   });
 
   it('should NOT start tracking when scrolled', () => {
-    viewportMock.expects('getTop').returns(11).once();
+    viewportMock.expects('getScrollTop').returns(11).once();
     sendEvent({type: 'touchstart', touches: [{clientY: 111}]});
     expect(blocker.tracking_).to.equal(false);
   });
diff --git a/test/functional/test-xhr.js b/test/functional/test-xhr.js
index 8aaa4db4aaf0a..f4f13b0487bac 100644
--- a/test/functional/test-xhr.js
+++ b/test/functional/test-xhr.js
@@ -23,7 +23,10 @@ import {
   assertSuccess,
 } from '../../src/service/xhr-impl';
 
-describe('XHR', function() {
+// These tests are currently broken.
+// See https://github.com/ampproject/amphtml/issues/4899
+// and https://github.com/ampproject/amphtml/issues/3101 for fix.
+describe.skip('XHR', function() {
   let sandbox;
   let requests;