diff --git a/build-system/tasks/compile.js b/build-system/tasks/compile.js
index e73c7d9709ec..7787dd2db07d 100644
--- a/build-system/tasks/compile.js
+++ b/build-system/tasks/compile.js
@@ -154,6 +154,8 @@ function compile(entryModuleFilenames, outputDir,
       'extensions/amp-bind/**/*.js',
       // Needed to access form impl from other extensions
       'extensions/amp-form/**/*.js',
+      // Needed to access UserNotificationManager from other extensions
+      'extensions/amp-user-notification/**/*.js',
       'src/*.js',
       'src/!(inabox)*/**/*.js',
       '!third_party/babel/custom-babel-helpers.js',
@@ -274,6 +276,7 @@ function compile(entryModuleFilenames, outputDir,
           'third_party/caja/',
           'third_party/closure-library/sha384-generated.js',
           'third_party/d3/',
+          'third_party/mustache/',
           'third_party/vega/',
           'third_party/webcomponentsjs/',
           'node_modules/',
diff --git a/extensions/amp-3q-player/0.1/amp-3q-player.js b/extensions/amp-3q-player/0.1/amp-3q-player.js
index a6d6ceb65c31..cbc1b089128b 100644
--- a/extensions/amp-3q-player/0.1/amp-3q-player.js
+++ b/extensions/amp-3q-player/0.1/amp-3q-player.js
@@ -16,13 +16,13 @@
 
 import {isLayoutSizeDefined} from '../../../src/layout';
 import {tryParseJson} from '../../../src/json';
-import {user} from '../../../src/log';
+import {user, dev} from '../../../src/log';
 import {removeElement} from '../../../src/dom';
 import {
   installVideoManagerForDoc,
 } from '../../../src/service/video-manager-impl';
 import {isObject} from '../../../src/types';
-import {listen} from '../../../src/event-helper';
+import {listen, getData} from '../../../src/event-helper';
 import {VideoEvents} from '../../../src/video-interface';
 import {videoManagerForDoc} from '../../../src/services';
 
@@ -89,8 +89,9 @@ class Amp3QPlayer extends AMP.BaseElement {
     );
 
     this.applyFillContent(iframe, true);
-    iframe.src = 'https://playout.3qsdn.com/' +
-      encodeURIComponent(this.dataId) + '?autoplay=false&amp=true';
+    iframe.src = 'https://playout.3qsdn.com/'
+        + encodeURIComponent(dev().assertString(this.dataId))
+        + '?autoplay=false&amp=true';
     this.element.appendChild(iframe);
 
     return this.loadPromise(this.iframe_).then(() =>
@@ -138,12 +139,14 @@ class Amp3QPlayer extends AMP.BaseElement {
       }
     }
 
-    const data = isObject(event.data) ? event.data : tryParseJson(event.data);
+    const data = isObject(getData(event))
+        ? getData(event)
+        : tryParseJson(getData(event));
     if (data === undefined) {
       return;
     }
 
-    switch (data.data) {
+    switch (data['data']) {
       case 'ready':
         this.element.dispatchCustomEvent(VideoEvents.LOAD);
         this.playerReadyResolver_();
diff --git a/extensions/amp-analytics/0.1/amp-analytics.js b/extensions/amp-analytics/0.1/amp-analytics.js
index 92a2c195632c..6180416f243e 100644
--- a/extensions/amp-analytics/0.1/amp-analytics.js
+++ b/extensions/amp-analytics/0.1/amp-analytics.js
@@ -145,7 +145,8 @@ export class AmpAnalytics extends AMP.BaseElement {
 
     if (this.consentNotificationId_ != null) {
       this.consentPromise_ = userNotificationManagerFor(this.win)
-          .then(service => service.get(this.consentNotificationId_));
+          .then(service => service.get(dev().assertString(
+              this.consentNotificationId_)));
     }
 
     if (this.element.getAttribute('trigger') == 'immediate') {
diff --git a/extensions/amp-apester-media/0.1/amp-apester-media.js b/extensions/amp-apester-media/0.1/amp-apester-media.js
index 751f86d85f46..d238981e2e6f 100644
--- a/extensions/amp-apester-media/0.1/amp-apester-media.js
+++ b/extensions/amp-apester-media/0.1/amp-apester-media.js
@@ -28,7 +28,48 @@ const TAG = 'amp-apester-media';
  * AMP Apester-media
  */
 class AmpApesterMedia extends AMP.BaseElement {
-  /** @override */
+
+  /** @param {!AmpElement} element */
+  constructor(element) {
+    super(element);
+    /**
+     * @const @private {string}
+     */
+    this.rendererBaseUrl_ = 'https://renderer.qmerce.com';
+
+    /**
+     * @const @private {string}
+     */
+    this.displayBaseUrl_ = 'https://display.apester.com';
+
+    /**
+     * @const @private {string}
+     */
+    this.loaderUrl_ = 'https://images.apester.com/images%2Floader.gif';
+    /** @private {boolean}  */
+    this.seen_ = false;
+    /** @private {?Element}  */
+    this.iframe_ = null;
+    /** @private {?Promise}  */
+    this.iframePromise_ = null;
+    /** @private {boolean}  */
+    this.ready_ = false;
+    /** @private {?number|undefined}  */
+    this.width_ = null;
+    /** @private {?number|undefined}  */
+    this.height_ = null;
+    /** @private {boolean}  */
+    this.random_ = false;
+    /**
+     * @private {?string}
+     */
+    this.mediaAttribute_ = null;
+  }
+
+  /**
+   * @param {boolean=} onLayout
+   * @override
+   */
   preconnectCallback(onLayout) {
     this.preconnect.url(this.displayBaseUrl_, onLayout);
     this.preconnect.url(this.rendererBaseUrl_, onLayout);
@@ -57,40 +98,9 @@ class AmpApesterMedia extends AMP.BaseElement {
   buildCallback() {
     const width = this.element.getAttribute('width');
     const height = this.element.getAttribute('height');
-
-    /**
-     *  @private @const {number}
-     *  */
     this.width_ = getLengthNumeral(width);
-
-    /**
-     * @private @const {number}
-     * */
     this.height_ = getLengthNumeral(height);
-
-    /**
-     * @const @private {string}
-     */
-    this.rendererBaseUrl_ = 'https://renderer.qmerce.com';
-
-    /**
-     * @const @private {string}
-     */
-    this.displayBaseUrl_ = 'https://display.apester.com';
-
-    /**
-     * @const @private {string}
-     */
-    this.loaderUrl_ = 'https://images.apester.com/images%2Floader.gif';
-
-    /**
-     * @private {boolean}
-     */
     this.random_ = false;
-
-    /**
-     * @const @private {string}
-     */
     this.mediaAttribute_ = user().assert(
         (this.element.getAttribute('data-apester-media-id') ||
          (this.random_ =
@@ -98,26 +108,6 @@ class AmpApesterMedia extends AMP.BaseElement {
         'Either the data-apester-media-id or the data-apester-channel-token ' +
         'attributes must be specified for <amp-apester-media> %s',
         this.element);
-
-    /**
-     * @private {?Element}
-     */
-    this.iframe_ = null;
-
-    /**
-     * @private {?Promise}
-     */
-    this.iframePromise_ = null;
-
-    /**
-     * @private {boolean}
-     */
-    this.seen_ = false;
-
-    /**
-     * @private {boolean}
-     */
-    this.ready_ = false;
   }
 
   /** @override */
@@ -131,7 +121,8 @@ class AmpApesterMedia extends AMP.BaseElement {
    * @return {string}
    **/
   buildUrl_() {
-    const encodedMediaAttribute = encodeURIComponent(this.mediaAttribute_);
+    const encodedMediaAttribute = encodeURIComponent(
+        dev().assertString(this.mediaAttribute_));
     const suffix = (this.random_) ?
         `/tokens/${encodedMediaAttribute}/interactions/random` :
         `/interactions/${encodedMediaAttribute}/display`;
@@ -241,9 +232,9 @@ class AmpApesterMedia extends AMP.BaseElement {
     this.element.classList.add('amp-apester-container');
     return this.queryMedia_()
         .then(response => {
-          const media = response.payload;
+          const media = response['payload'];
           const src = this.constructUrlFromMedia_(
-              media.interactionId);
+              media['interactionId']);
           const iframe = this.constructIframe_(src);
           const overflow = this.constructOverflow_();
           const mutate = state => {
@@ -262,10 +253,12 @@ class AmpApesterMedia extends AMP.BaseElement {
         }, error => {
           dev().error(TAG, 'Display', error);
           return undefined;
-        }).then(media => {
+        })
+        /** @param {!JsonObject} media */
+        .then(media => {
           this.togglePlaceholder(false);
           this.ready_ = true;
-          const height = 0 || media.data.size.height;
+          const height = 0 || media['data']['size']['height'];
           if (height != this.height_) {
             this.height_ = height;
             if (this.random_) {
diff --git a/extensions/amp-experiment/0.1/amp-experiment.js b/extensions/amp-experiment/0.1/amp-experiment.js
index ce915e454cd8..33d667e27638 100644
--- a/extensions/amp-experiment/0.1/amp-experiment.js
+++ b/extensions/amp-experiment/0.1/amp-experiment.js
@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-import {user} from '../../../src/log';
+import {dev, user} from '../../../src/log';
+import {parseJson} from '../../../src/json';
 import {Layout} from '../../../src/layout';
 import {waitForBodyPromise} from '../../../src/dom';
 import {allocateVariant} from './variant';
@@ -53,6 +54,7 @@ export class AmpExperiment extends AMP.BaseElement {
     });
   }
 
+  /** @return {!JsonObject} [description] */
   getConfig_() {
     const children = this.element.children;
     user().assert(
@@ -62,7 +64,8 @@ export class AmpExperiment extends AMP.BaseElement {
         '<amp-experiment> should contain exactly one ' +
         '<script type="application/json"> child.');
 
-    return JSON.parse(children[0].textContent);
+    return /** @type {!JsonObject} */ (
+        dev().assert(parseJson(children[0].textContent)));
   }
 
   /**
@@ -78,7 +81,8 @@ export class AmpExperiment extends AMP.BaseElement {
     return waitForBodyPromise(doc).then(() => {
       for (const name in experiments) {
         if (experiments[name]) {
-          doc.body.setAttribute(ATTR_PREFIX + name, experiments[name]);
+          doc.body.setAttribute(ATTR_PREFIX + name,
+              dev().assertString(experiments[name]));
         }
       }
       return experiments;
diff --git a/extensions/amp-experiment/0.1/variant.js b/extensions/amp-experiment/0.1/variant.js
index ba21b2932250..712383380a26 100644
--- a/extensions/amp-experiment/0.1/variant.js
+++ b/extensions/amp-experiment/0.1/variant.js
@@ -15,7 +15,7 @@
  */
 
 import {isObject} from '../../../src/types';
-import {user} from '../../../src/log';
+import {dev, user} from '../../../src/log';
 import {cidForDoc} from '../../../src/services';
 import {viewerForDoc} from '../../../src/services';
 import {userNotificationManagerFor} from '../../../src/services';
@@ -29,7 +29,7 @@ const nameValidator = /^[\w-]+$/;
  * experiment config.
  * @param {!../../../src/service/ampdoc-impl.AmpDoc} ampdoc
  * @param {string} experimentName
- * @param {!Object} config
+ * @param {!JsonObject} config
  * @return {!Promise<?string>}
  */
 export function allocateVariant(ampdoc, experimentName, config) {
@@ -39,21 +39,22 @@ export function allocateVariant(ampdoc, experimentName, config) {
   // Variant can be overridden from URL fragment.
   const viewer = viewerForDoc(ampdoc);
   const override = viewer.getParam(ATTR_PREFIX + experimentName);
-  if (override && config.variants.hasOwnProperty(override)) {
-    return Promise.resolve(override);
+  if (override && config['variants'].hasOwnProperty(override)) {
+    return Promise.resolve(/** @type {?string} */ (override));
   }
 
-  const sticky = config.sticky !== false;
-  const cidScope = config.cidScope || 'amp-experiment';
+  const sticky = config['sticky'] !== false;
+  const cidScope = config['cidScope'] || 'amp-experiment';
 
   let hasConsentPromise = Promise.resolve(true);
 
-  if (sticky && config.consentNotificationId) {
+  if (sticky && config['consentNotificationId']) {
     hasConsentPromise = userNotificationManagerFor(ampdoc.win)
-        .then(manager => manager.getNotification(config.consentNotificationId))
+        .then(manager => manager.getNotification(
+            config['consentNotificationId']))
         .then(userNotification => {
           user().assert(userNotification,
-              `Notification not found: ${config.consentNotificationId}`);
+              `Notification not found: ${config['consentNotificationId']}`);
           return userNotification.isDismissed();
         });
   }
@@ -62,16 +63,16 @@ export function allocateVariant(ampdoc, experimentName, config) {
     if (!hasConsent) {
       return null;
     }
-    const group = config.group || experimentName;
+    const group = config['group'] || experimentName;
     return getBucketTicket(ampdoc, group, sticky ? cidScope : null)
         .then(ticket => {
           let upperBound = 0;
 
           // Loop through keys in a specific order since the default object key
           // enumeration is implementation (browser) dependent.
-          const variantNames = Object.keys(config.variants).sort();
+          const variantNames = Object.keys(config['variants']).sort();
           for (let i = 0; i < variantNames.length; i++) {
-            upperBound += config.variants[variantNames[i]];
+            upperBound += config['variants'][variantNames[i]];
             if (ticket < upperBound) {
               return variantNames[i];
             }
@@ -83,15 +84,15 @@ export function allocateVariant(ampdoc, experimentName, config) {
 
 /**
  * Validates an experiment config.
- * @param {!Object} config
+ * @param {!JsonObject} config
  * @throws {!Error}
  */
 function validateConfig(config) {
-  const variants = config.variants;
+  const variants = config['variants'];
   user().assert(isObject(variants) && Object.keys(variants).length > 0,
       'Missing experiment variants config.');
-  if (config.group) {
-    assertName(config.group);
+  if (config['group']) {
+    assertName(config['group']);
   }
   let totalPercentage = 0;
   for (const variantName in variants) {
@@ -124,9 +125,10 @@ function getBucketTicket(ampdoc, group, opt_cidScope) {
     return Promise.resolve(ampdoc.win.Math.random() * 100);
   }
 
-  const cidPromise = cidForDoc(ampdoc).then(cidService => cidService.get(
-        {scope: opt_cidScope, createCookieIfNotPresent: true},
-      Promise.resolve()));
+  const cidPromise = cidForDoc(ampdoc).then(cidService => cidService.get({
+    scope: dev().assertString(opt_cidScope),
+    createCookieIfNotPresent: true,
+  }, Promise.resolve()));
 
   return Promise.all([cidPromise, cryptoFor(ampdoc.win)])
       .then(results => results[1].uniform(group + ':' + results[0]))
diff --git a/extensions/amp-fit-text/0.1/amp-fit-text.js b/extensions/amp-fit-text/0.1/amp-fit-text.js
index 86131627ee9a..6fc99aa93958 100644
--- a/extensions/amp-fit-text/0.1/amp-fit-text.js
+++ b/extensions/amp-fit-text/0.1/amp-fit-text.js
@@ -25,6 +25,26 @@ const LINE_HEIGHT_EM_ = 1.15;
 
 class AmpFitText extends AMP.BaseElement {
 
+  /** @param {!AmpElement} element */
+  constructor(element) {
+    super(element);
+
+    /** @private {?Element} */
+    this.content_ = null;
+
+    /** @private {?Element} */
+    this.contentWrapper_ = null;
+
+    /** @private {?Element} */
+    this.measurer_ = null;
+
+    /** @private {number} */
+    this.minFontSize_ = -1;
+
+    /** @private {number} */
+    this.maxFontSize_ = -1;
+  }
+
   /** @override */
   isLayoutSupported(layout) {
     return isLayoutSizeDefined(layout);
@@ -32,19 +52,15 @@ class AmpFitText extends AMP.BaseElement {
 
   /** @override */
   buildCallback() {
-
-    /** @private @const */
     this.content_ = this.element.ownerDocument.createElement('div');
     this.applyFillContent(this.content_);
     this.content_.classList.add('i-amphtml-fit-text-content');
     st.setStyles(this.content_, {zIndex: 2});
 
-    /** @private @const */
     this.contentWrapper_ = this.element.ownerDocument.createElement('div');
     st.setStyles(this.contentWrapper_, {lineHeight: `${LINE_HEIGHT_EM_}em`});
     this.content_.appendChild(this.contentWrapper_);
 
-    /** @private @const */
     this.measurer_ = this.element.ownerDocument.createElement('div');
     // Note that "measurer" cannot be styled with "bottom:0".
     st.setStyles(this.measurer_, {
@@ -63,11 +79,9 @@ class AmpFitText extends AMP.BaseElement {
     this.element.appendChild(this.content_);
     this.element.appendChild(this.measurer_);
 
-    /** @private @const {number} */
     this.minFontSize_ = getLengthNumeral(this.element.getAttribute(
         'min-font-size')) || 6;
 
-    /** @private @const {number} */
     this.maxFontSize_ = getLengthNumeral(this.element.getAttribute(
         'max-font-size')) || 72;
   }
@@ -102,7 +116,7 @@ class AmpFitText extends AMP.BaseElement {
 
 
 /**
- * @param {!Element} measurer
+ * @param {Element} measurer
  * @param {number} expectedHeight
  * @param {number} minFontSize
  * @param {number} maxFontSize
@@ -129,8 +143,8 @@ export function calculateFontSize_(measurer, expectedHeight, expectedWidth,
 
 
 /**
- * @param {!Element} content
- * @param {!Element} measurer
+ * @param {Element} content
+ * @param {Element} measurer
  * @param {number} maxHeight
  * @param {number} fontSize
  * @private  Visible for testing only!
diff --git a/extensions/amp-font/0.1/amp-font.js b/extensions/amp-font/0.1/amp-font.js
index c57960f8c19a..4675f502207e 100644
--- a/extensions/amp-font/0.1/amp-font.js
+++ b/extensions/amp-font/0.1/amp-font.js
@@ -79,6 +79,25 @@ const CACHED_FONT_LOAD_TIME_ = 100;
 
 export class AmpFont extends AMP.BaseElement {
 
+  /** @param {!AmpElement} element */
+  constructor(element) {
+    super(element);
+
+    /** @private {string} */
+    this.fontFamily_ = '';
+    /** @private {string} */
+    this.fontWeight_ = '';
+    /** @private {string} */
+    this.fontStyle_ = '';
+    /** @private {string} */
+    this.fontVariant_ = '';
+    /** @private {?Document} */
+    this.document_ = null;
+    /** @private {?Element} */
+    this.documentElement_ = null;
+    /** @private {?FontLoader} */
+    this.fontLoader_ = null;
+  }
 
   /** @override */
   prerenderAllowed() {
@@ -88,24 +107,17 @@ export class AmpFont extends AMP.BaseElement {
 
   /** @override */
   buildCallback() {
-    /** @private @const {string} */
     this.fontFamily_ = user().assert(this.element.getAttribute('font-family'),
         'The font-family attribute is required for <amp-font> %s',
         this.element);
-    /** @private @const {string} */
     this.fontWeight_ =
         this.element.getAttribute('font-weight') || DEFAULT_WEIGHT_;
-    /** @private @const {string} */
     this.fontStyle_ =
         this.element.getAttribute('font-style') || DEFAULT_STYLE_;
-    /** @private @const {string} */
     this.fontVariant_ =
         this.element.getAttribute('font-variant') || DEFAULT_VARIANT_;
-    /** @private @const {!Document} */
     this.document_ = this.win.document;
-    /** @private @const {!Element} */
     this.documentElement_ = this.document_.documentElement;
-    /** @private @const {!FontLoader} */
     this.fontLoader_ = new FontLoader(this.win);
     this.startLoad_();
   }
@@ -116,7 +128,6 @@ export class AmpFont extends AMP.BaseElement {
    * @private
    */
   startLoad_() {
-    /** @type FontConfig */
     const fontConfig = {
       style: this.fontStyle_,
       variant: this.fontVariant_,
diff --git a/extensions/amp-font/0.1/fontloader.js b/extensions/amp-font/0.1/fontloader.js
index 8746bbf0ffbd..5dd1ff3cd3ed 100644
--- a/extensions/amp-font/0.1/fontloader.js
+++ b/extensions/amp-font/0.1/fontloader.js
@@ -59,7 +59,7 @@ export class FontLoader {
     this.fontLoadResolved_ = false;
     /** @private {boolean} */
     this.fontLoadRejected_ = false;
-    /** @private {FontConfigDef} */
+    /** @private {?FontConfigDef} */
     this.fontConfig_ = null;
   }
 
@@ -239,7 +239,7 @@ class FontComparator {
 
   /**
    * Create and style a DOM element to use to compare two fonts.
-   * @param {!Document} doc
+   * @param {?Document} doc
    * @param {string} fontFamily
    * @return {!Element}
    * @private
diff --git a/extensions/amp-google-vrview-image/0.1/amp-google-vrview-image.js b/extensions/amp-google-vrview-image/0.1/amp-google-vrview-image.js
index 1587a3856361..11a5219b3748 100644
--- a/extensions/amp-google-vrview-image/0.1/amp-google-vrview-image.js
+++ b/extensions/amp-google-vrview-image/0.1/amp-google-vrview-image.js
@@ -24,6 +24,23 @@ const TAG = 'amp-google-vrview-image';
 
 class AmpGoogleVrviewImage extends AMP.BaseElement {
 
+  /** @param {!AmpElement} element */
+  constructor(element) {
+    super(element);
+
+    /** @private {boolean} */
+    this.isExperimentOn_ = false;
+
+    /** @private {string} */
+    this.imageSrc_ = '';
+
+    /** @private {string} */
+    this.src_ = '';
+
+    /** @private {?Element} */
+    this.iframe_ = null;
+  }
+
   /** @override */
   isLayoutSupported(layout) {
     return isLayoutSizeDefined(layout);
@@ -31,14 +48,12 @@ class AmpGoogleVrviewImage extends AMP.BaseElement {
 
   /** @override */
   buildCallback() {
-    /** @const @private {boolean} */
     this.isExperimentOn_ = isExperimentOn(this.win, TAG);
     if (!this.isExperimentOn_) {
       dev().warn(TAG, `TAG ${TAG} disabled`);
       return;
     }
 
-    /** @private @const {string} */
     this.imageSrc_ = assertHttpsUrl(this.element.getAttribute('src'),
         this.element);
     // TODO(dvoytenko): Consider recompiling and hosting viewer on the
@@ -56,7 +71,6 @@ class AmpGoogleVrviewImage extends AMP.BaseElement {
     if (this.element.hasAttribute('yaw-only')) {
       src = addParamToUrl(src, 'is_yaw_only', 'true');
     }
-    /** @private @const {string} */
     this.src_ = src;
   }
 
@@ -93,10 +107,7 @@ class AmpGoogleVrviewImage extends AMP.BaseElement {
     iframe.setAttribute('allowfullscreen', 'true');
     iframe.setAttribute('src', this.src_);
     this.element.appendChild(iframe);
-
-    /** @private {!Element} */
     this.iframe_ = iframe;
-
     return this.loadPromise(iframe);
   }
 }
diff --git a/extensions/amp-iframe/0.1/amp-iframe.js b/extensions/amp-iframe/0.1/amp-iframe.js
index 78b52ea588fb..1123491fb7ad 100644
--- a/extensions/amp-iframe/0.1/amp-iframe.js
+++ b/extensions/amp-iframe/0.1/amp-iframe.js
@@ -54,6 +54,60 @@ let trackingIframeCount = 0;
 let trackingIframeTimeout = 5000;
 
 export class AmpIframe extends AMP.BaseElement {
+
+  /** @param {!AmpElement} element */
+  constructor(element) {
+    super(element);
+    /** @private {?Element} */
+    this.placeholder_ = null;
+
+    /** @private {boolean} */
+    this.isClickToPlay_ = false;
+
+    /** @private {boolean} */
+    this.isAdLike_ = false;
+
+    /** @private {boolean} */
+    this.isTrackingFrame_ = false;
+
+    /** @private {boolean} */
+    this.isDisallowedAsAd_ = false;
+
+    /**
+     * Call to stop listening to viewport changes.
+     * @private {?function()}
+     */
+    this.unlistenViewportChanges_ = null;
+
+    /**
+     * The (relative) layout box of the ad iframe to the amp-ad tag.
+     * @private {?../../../src/layout-rect.LayoutRectDef}
+     */
+    this.iframeLayoutBox_ = null;
+
+    /** @private  {?HTMLIFrameElement} */
+    this.iframe_ = null;
+
+    /** @private {boolean} */
+    this.isResizable_ = false;
+
+    /** @private {?IntersectionObserverApi} */
+    this.intersectionObserverApi_ = null;
+
+    /** @private {string} */
+    this.sandbox_ = '';
+
+    /**
+     * The source of the iframe. May change to null for tracking iframes
+     * to prevent them from being recreated.
+     * @type {?string}
+     **/
+    this.iframeSrc = null;
+
+    /** @private {?Element} */
+    this.container_ = null;
+  }
+
   /** @override */
   isLayoutSupported(layout) {
     return isLayoutSizeDefined(layout);
@@ -149,18 +203,12 @@ export class AmpIframe extends AMP.BaseElement {
 
   /** @override */
   firstAttachedCallback() {
-    /** @private @const {string} */
     this.sandbox_ = this.element.getAttribute('sandbox');
 
     const iframeSrc =
         this.transformSrc_(this.element.getAttribute('src')) ||
         this.transformSrcDoc_(
             this.element.getAttribute('srcdoc'), this.sandbox_);
-    /**
-     * The source of the iframe. May later be set to null for tracking iframes
-     * to prevent them from being recreated.
-     * @type {?string}
-     **/
     this.iframeSrc = this.assertSource(
         iframeSrc, window.location.href, this.sandbox_);
 
@@ -172,7 +220,10 @@ export class AmpIframe extends AMP.BaseElement {
     this.container_ = makeIOsScrollable(this.element);
   }
 
-  /** @override */
+  /**
+   * @param {boolean=} onLayout
+   * @override
+   */
   preconnectCallback(onLayout) {
     if (this.iframeSrc) {
       this.preconnect.url(this.iframeSrc, onLayout);
@@ -181,45 +232,13 @@ export class AmpIframe extends AMP.BaseElement {
 
   /** @override */
   buildCallback() {
-    /** @private @const {!Element} */
     this.placeholder_ = this.getPlaceholder();
-
-    /** @private @const {boolean} */
     this.isClickToPlay_ = !!this.placeholder_;
-
-    /** @private {boolean} */
-    this.isAdLike_ = false;
-
-    /** @private {boolean} */
-    this.isTrackingFrame_ = false;
-
-    /** @private {boolean} */
-    this.isDisallowedAsAd_ = false;
-
-    /**
-     * Call to stop listening to viewport changes.
-     * @private {?function()}
-     */
-    this.unlistenViewportChanges_ = null;
-
-    /**
-     * The (relative) layout box of the ad iframe to the amp-ad tag.
-     * @private {?../../../src/layout-rect.LayoutRectDef}
-     */
-    this.iframeLayoutBox_ = null;
-
-    /** @private  {?HTMLIFrameElement} */
-    this.iframe_ = null;
-
-    /** @private @const {boolean} */
     this.isResizable_ = this.element.hasAttribute('resizable');
     if (this.isResizable_) {
       this.element.setAttribute('scrolling', 'no');
     }
 
-    /** @private {?IntersectionObserverApi} */
-    this.intersectionObserverApi_ = null;
-
     if (!this.element.hasAttribute('frameborder')) {
       this.element.setAttribute('frameborder', '0');
     }
@@ -347,7 +366,7 @@ export class AmpIframe extends AMP.BaseElement {
     };
 
     listenFor(iframe, 'embed-size', data => {
-      this.updateSize_(data.height, data.width);
+      this.updateSize_(data['height'], data['width']);
     });
 
     if (this.isClickToPlay_) {
diff --git a/extensions/amp-lightbox-viewer/0.1/amp-lightbox-viewer.js b/extensions/amp-lightbox-viewer/0.1/amp-lightbox-viewer.js
index a6e0364745d1..cf1ec31b2a84 100644
--- a/extensions/amp-lightbox-viewer/0.1/amp-lightbox-viewer.js
+++ b/extensions/amp-lightbox-viewer/0.1/amp-lightbox-viewer.js
@@ -23,7 +23,7 @@ import {Layout} from '../../../src/layout';
 import {user, dev} from '../../../src/log';
 import {extensionsFor} from '../../../src/services';
 import {toggle, setStyle} from '../../../src/style';
-import {listen} from '../../../src/event-helper';
+import {getData, listen} from '../../../src/event-helper';
 import {LightboxManager} from './service/lightbox-manager-impl';
 
 /** @const */
@@ -40,20 +40,9 @@ let manager_;
  */
 export class AmpLightboxViewer extends AMP.BaseElement {
 
-  /** @override */
-  isLayoutSupported(layout) {
-    return layout == Layout.NODISPLAY;
-  }
-
-  /** @override */
-  renderOutsideViewport() {
-    return true;
-  }
-
-  /** @override */
-  buildCallback() {
-    user().assert(isExperimentOn(this.win, TAG),
-        `Experiment ${TAG} disabled`);
+  /** @param {!AmpElement} element */
+  constructor(element) {
+    super(element);
 
     /** @private {!boolean} */
     this.active_ = false;
@@ -65,18 +54,17 @@ export class AmpLightboxViewer extends AMP.BaseElement {
     this.boundHandleKeyboardEvents_ = this.handleKeyboardEvents_.bind(this);
 
     /**
-     * @const
-     * @private {!./service/lightbox-manager-impl.LightboxManager}
+     * @private {?./service/lightbox-manager-impl.LightboxManager}
      */
-    this.manager_ = dev().assert(manager_);
+    this.manager_ = null;
 
-    /** @const @private {!Vsync} */
-    this.vsync_ = this.getVsync();
+    /** @private {?../../../src/service/vsync-impl.Vsync} */
+    this.vsync_ = null;
 
-    /** @const @private {!Element} */
-    this.container_ = this.win.document.createElement('div');
-    this.container_.classList.add('i-amphtml-lbv');
+    /** @private {?Element} */
+    this.container_ = null;
 
+    /** @private {?Element} */
     this.carousel_ = null;
 
     /** @private {?Element} */
@@ -94,6 +82,29 @@ export class AmpLightboxViewer extends AMP.BaseElement {
     /** @private {?Array<{string, Element}>} */
     this.thumbnails_ = null;
 
+    /** @private  {?Element} */
+    this.topBar_ = null;
+  }
+
+  /** @override */
+  isLayoutSupported(layout) {
+    return layout == Layout.NODISPLAY;
+  }
+
+  /** @override */
+  renderOutsideViewport() {
+    return true;
+  }
+
+  /** @override */
+  buildCallback() {
+    user().assert(isExperimentOn(this.win, TAG),
+        `Experiment ${TAG} disabled`);
+    this.manager_ = dev().assert(manager_);
+    this.vsync_ = this.getVsync();
+    this.container_ = this.win.document.createElement('div');
+    this.container_.classList.add('i-amphtml-lbv');
+
     this.buildMask_();
     this.buildCarousel_();
     this.buildDescriptionBox_();
@@ -167,7 +178,7 @@ export class AmpLightboxViewer extends AMP.BaseElement {
    * @private
    */
   slideChangeHandler_(event) {
-    this.currentElementId_ = event.data.index;
+    this.currentElementId_ = getData(event)['index'];
     this.updateDescriptionBox_();
   }
 
@@ -176,7 +187,7 @@ export class AmpLightboxViewer extends AMP.BaseElement {
    * @private
    */
   buildDescriptionBox_() {
-    dev().assert(this.container_);
+
     this.descriptionBox_ = this.win.document.createElement('div');
     this.descriptionBox_.classList.add('i-amphtml-lbv-desc-box');
     this.descriptionBox_.classList.add('standard');
@@ -186,7 +197,7 @@ export class AmpLightboxViewer extends AMP.BaseElement {
     this.descriptionBox_.appendChild(this.descriptionTextArea_);
 
     const toggleDescription = this.toggleDescriptionBox_.bind(this);
-    listen(this.container_, 'click', toggleDescription);
+    listen(dev().assertElement(this.container_), 'click', toggleDescription);
     this.descriptionBox_.addEventListener('click', event => {
       this.toggleDescriptionOverflow_();
       event.stopPropagation();
@@ -276,7 +287,7 @@ export class AmpLightboxViewer extends AMP.BaseElement {
     this.buildButton_('Content', 'amp-lbv-button-slide', closeGallery);
 
     const toggleTopBar = this.toggleTopBar_.bind(this);
-    listen(this.container_, 'click', toggleTopBar);
+    listen(dev().assertElement(this.container_), 'click', toggleTopBar);
     this.container_.appendChild(this.topBar_);
   }
 
@@ -312,17 +323,17 @@ export class AmpLightboxViewer extends AMP.BaseElement {
    *  // Opens the element referenced by elementId
    *  on="tap:myLightboxViewer.open(id='<elementId>')
    * @override
-   * @return {!Promise}
+   * @param {!../../../src/service/action-impl.ActionInvocation} invocation
    */
   activate(invocation) {
     let target = invocation.source;
-    if (invocation.args && invocation.args.id) {
-      const targetId = invocation.args.id;
+    if (invocation.args && invocation.args['id']) {
+      const targetId = invocation.args['id'];
       target = this.win.document.getElementById(targetId);
       user().assert(target,
           'amp-lightbox-viewer.open: element with id: %s not found', targetId);
     }
-    return this.open_(target);
+    return this.open_(dev().assertElement(target));
   }
 
   /**
@@ -337,11 +348,14 @@ export class AmpLightboxViewer extends AMP.BaseElement {
     toggle(this.element, true);
     this.active_ = true;
 
-    this.updateInViewport(this.container_, true);
-    this.scheduleLayout(this.container_);
+    this.updateInViewport(dev().assertElement(this.container_), true);
+    this.scheduleLayout(dev().assertElement(this.container_));
 
     this.currentElementId_ = element.lightboxItemId;
-    this.carousel_.implementation_.showSlideWhenReady(this.currentElementId_);
+    // Hack to access private property. Better than not getting
+    // type checking to work.
+    /**@type {?}*/ (this.carousel_).implementation_.showSlideWhenReady(
+        this.currentElementId_);
 
     this.win.document.documentElement.addEventListener(
         'keydown', this.boundHandleKeyboardEvents_);
@@ -377,19 +391,12 @@ export class AmpLightboxViewer extends AMP.BaseElement {
   /**
    * Handles keyboard events for the lightbox.
    *  -Esc will close the lightbox.
-   *  -Right arrow goes to next
-   *  -Left arrow goes to previous
    * @private
    */
   handleKeyboardEvents_(event) {
-    // TODO(aghassemi): RTL support
     const code = event.keyCode;
     if (code == KeyCodes.ESCAPE) {
       this.close_();
-    } else if (code == KeyCodes.RIGHT_ARROW) {
-      this.next_();
-    } else if (code == KeyCodes.LEFT_ARROW) {
-      this.previous_();
     }
   }
 
@@ -458,7 +465,7 @@ export class AmpLightboxViewer extends AMP.BaseElement {
 
   /**
    * Create an element inside gallery from the thumbnail info from manager.
-   * @param {{string, Element}} thumbnailObj
+   * @param {{url: string, element: !Element}} thumbnailObj
    * @private
    */
   createThumbnailElement_(thumbnailObj) {
@@ -472,7 +479,10 @@ export class AmpLightboxViewer extends AMP.BaseElement {
       this.closeGallery_();
       this.currentElementId_ = thumbnailObj.element.lightboxItemId;
       this.updateDescriptionBox_();
-      this.carousel_.implementation_.showSlideWhenReady(this.currentElementId_);
+      // Hack to access private property. Better than not getting
+      // type checking to work.
+      /**@type {?}*/ (this.carousel_).implementation_.showSlideWhenReady(
+          this.currentElementId_);
       event.stopPropagation();
     };
     element.addEventListener('click', closeGallaryAndShowTargetSlide);
diff --git a/extensions/amp-lightbox-viewer/0.1/service/lightbox-manager-discovery.js b/extensions/amp-lightbox-viewer/0.1/service/lightbox-manager-discovery.js
index fa2570be1d0c..6c0941a65686 100644
--- a/extensions/amp-lightbox-viewer/0.1/service/lightbox-manager-discovery.js
+++ b/extensions/amp-lightbox-viewer/0.1/service/lightbox-manager-discovery.js
@@ -124,25 +124,26 @@ function meetsHeuristicsForTap(element) {
 /**
  * Tries to find an existing amp-lightbox-viewer, if there is none, it adds a
  * default one.
- * @param {!Element} elem
- * @return {!string} Returns the id of the amp-lightbox-viewer.
+ * @param {!../../../../src/service/ampdoc-impl.AmpDoc} ampdoc
+ * @return {!Promise<string>} Returns the id of the amp-lightbox-viewer.
  */
 function maybeInstallLightboxViewer(ampdoc) {
   // TODO(aghassemi): Use the upcoming ampdoc.waitForBody
-  return waitForBodyPromise(ampdoc.getRootNode()).then(() => {
-    const existingViewer = elementByTag(ampdoc.getRootNode(), VIEWER_TAG);
-    if (existingViewer) {
-      if (!existingViewer.id) {
-        existingViewer.id = DEFAULT_VIEWER_ID;
-      }
-      return existingViewer.id;
-    }
-
-    const viewer = ampdoc.getRootNode().createElement(VIEWER_TAG);
-    viewer.setAttribute('layout', 'nodisplay');
-    viewer.setAttribute('id', DEFAULT_VIEWER_ID);
-    ampdoc.getRootNode().body.appendChild(viewer);
-
-    return viewer.id;
-  });
+  return waitForBodyPromise(/** @type {!Document} */ (
+      ampdoc.getRootNode())).then(() => {
+        const existingViewer = elementByTag(ampdoc.getRootNode(), VIEWER_TAG);
+        if (existingViewer) {
+          if (!existingViewer.id) {
+            existingViewer.id = DEFAULT_VIEWER_ID;
+          }
+          return existingViewer.id;
+        }
+
+        const viewer = ampdoc.getRootNode().createElement(VIEWER_TAG);
+        viewer.setAttribute('layout', 'nodisplay');
+        viewer.setAttribute('id', DEFAULT_VIEWER_ID);
+        ampdoc.getRootNode().body.appendChild(viewer);
+
+        return viewer.id;
+      });
 }
diff --git a/extensions/amp-lightbox-viewer/0.1/service/lightbox-manager-impl.js b/extensions/amp-lightbox-viewer/0.1/service/lightbox-manager-impl.js
index 6deb9c86173a..7dd8b4999844 100644
--- a/extensions/amp-lightbox-viewer/0.1/service/lightbox-manager-impl.js
+++ b/extensions/amp-lightbox-viewer/0.1/service/lightbox-manager-impl.js
@@ -148,7 +148,7 @@ export class LightboxManager {
    * @return {!Promise}
    */
   scanLightboxables_() {
-    return whenDocumentReady(this.ampdoc_).then(() => {
+    return whenDocumentReady(this.ampdoc_.win.document).then(() => {
       const matches = this.ampdoc_.getRootNode().querySelectorAll('[lightbox]');
       this.elements_ = [];
       for (let i = 0; i < matches.length; i++) {
@@ -193,7 +193,7 @@ export class LightboxManager {
    * The function is not implemented yet. Fake for testing.
    * Find or create thumbnails for lightboxed elements.
    * Return a list of thumbnails obj for lightbox gallery view
-   * @return {!Array<{string,Element}>}
+   * @return {!Array<{url: string, element: !Element}>}
    */
   getThumbnails() {
     const thumbnailList = [];
@@ -211,7 +211,7 @@ export class LightboxManager {
    * The function is not implemented yet. Fake for testing.
    * Get thumbnail url for single element.
    * @param {!Element} element
-   * @param {Number=} index fake it for testing only, will delete later
+   * @param {number=} index fake it for testing only, will delete later
    * @return {string}
    * @private
    */
diff --git a/extensions/amp-list/0.1/amp-list.js b/extensions/amp-list/0.1/amp-list.js
index bd3a0a344a63..f28c03c5a128 100644
--- a/extensions/amp-list/0.1/amp-list.js
+++ b/extensions/amp-list/0.1/amp-list.js
@@ -21,7 +21,7 @@ import {isArray} from '../../../src/types';
 import {isLayoutSizeDefined} from '../../../src/layout';
 import {removeChildren} from '../../../src/dom';
 import {templatesFor} from '../../../src/services';
-import {user} from '../../../src/log';
+import {dev, user} from '../../../src/log';
 
 /**
  * The implementation of `amp-list` component. See {@link ../amp-list.md} for
@@ -29,6 +29,14 @@ import {user} from '../../../src/log';
  */
 export class AmpList extends AMP.BaseElement {
 
+  /** @param {!AmpElement} element */
+  constructor(element) {
+    super(element);
+
+    /** @private {?Element} */
+    this.container_ = null;
+  }
+
   /** @override */
   isLayoutSupported(layout) {
     return isLayoutSizeDefined(layout);
@@ -36,7 +44,6 @@ export class AmpList extends AMP.BaseElement {
 
   /** @override */
   buildCallback() {
-    /** @const {!Element} */
     this.container_ = this.win.document.createElement('div');
     this.applyFillContent(this.container_, true);
     this.element.appendChild(this.container_);
@@ -100,7 +107,7 @@ export class AmpList extends AMP.BaseElement {
    * @private
    */
   rendered_(elements) {
-    removeChildren(this.container_);
+    removeChildren(dev().assertElement(this.container_));
     elements.forEach(element => {
       if (!element.hasAttribute('role')) {
         element.setAttribute('role', 'listitem');
diff --git a/extensions/amp-mustache/0.1/amp-mustache.js b/extensions/amp-mustache/0.1/amp-mustache.js
index 926e352f189f..0c61a30fb6f7 100644
--- a/extensions/amp-mustache/0.1/amp-mustache.js
+++ b/extensions/amp-mustache/0.1/amp-mustache.js
@@ -27,6 +27,7 @@ setUnescapedSanitizier(sanitizeFormattingHtml);
  * See {@link https://github.com/janl/mustache.js/}.
  *
  * @private Visible for testing.
+ * @extends {BaseTemplate$$module$src$service$template_impl}
  */
 export class AmpMustache extends AMP.BaseTemplate {
 
diff --git a/gulpfile.js b/gulpfile.js
index 4a321a05a59c..58002bb13900 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -47,7 +47,7 @@ var extensionAliasFilePath = {};
 
 // Each extension and version must be listed individually here.
 // NOTE: No new extensions must pass the NO_TYPE_CHECK argument.
-declareExtension('amp-3q-player', '0.1', false, 'NO_TYPE_CHECK');
+declareExtension('amp-3q-player', '0.1', false);
 declareExtension('amp-access', '0.1', true, 'NO_TYPE_CHECK');
 declareExtension('amp-access-laterpay', '0.1', true, 'NO_TYPE_CHECK');
 declareExtension('amp-accordion', '0.1', false);
@@ -62,7 +62,7 @@ declareExtension('amp-ad-exit', 0.1, false);
 declareExtension('amp-analytics', '0.1', false);
 declareExtension('amp-anim', '0.1', false);
 declareExtension('amp-animation', '0.1', false);
-declareExtension('amp-apester-media', '0.1', true, 'NO_TYPE_CHECK');
+declareExtension('amp-apester-media', '0.1', true);
 declareExtension('amp-app-banner', '0.1', true);
 declareExtension('amp-audio', '0.1', false);
 declareExtension('amp-auto-ads', '0.1', false);
@@ -74,13 +74,13 @@ declareExtension('amp-call-tracking', '0.1', false);
 declareExtension('amp-carousel', '0.1', true);
 declareExtension('amp-crypto-polyfill', '0.1', false);
 declareExtension('amp-dailymotion', '0.1', false);
-declareExtension('amp-dynamic-css-classes', '0.1', false, 'NO_TYPE_CHECK');
-declareExtension('amp-experiment', '0.1', false, 'NO_TYPE_CHECK');
+declareExtension('amp-dynamic-css-classes', '0.1', false);
+declareExtension('amp-experiment', '0.1', false);
 declareExtension('amp-facebook', '0.1', false);
 declareExtension('amp-facebook-comments', '0.1', false);
 declareExtension('amp-facebook-like', '0.1', false);
-declareExtension('amp-fit-text', '0.1', true, 'NO_TYPE_CHECK');
-declareExtension('amp-font', '0.1', false, 'NO_TYPE_CHECK');
+declareExtension('amp-fit-text', '0.1', true);
+declareExtension('amp-font', '0.1', false);
 declareExtension('amp-form', '0.1', true);
 declareExtension('amp-fresh', '0.1', true);
 declareExtension('amp-fx-flying-carpet', '0.1', true);
@@ -88,7 +88,7 @@ declareExtension('amp-fx-parallax', '0.1', false);
 declareExtension('amp-gfycat', '0.1', false);
 declareExtension('amp-gist', '0.1', false);
 declareExtension('amp-hulu', '0.1', false);
-declareExtension('amp-iframe', '0.1', false, 'NO_TYPE_CHECK');
+declareExtension('amp-iframe', '0.1', false);
 declareExtension('amp-ima-video', '0.1', false);
 declareExtension('amp-image-lightbox', '0.1', true);
 declareExtension('amp-imgur', '0.1', false);
@@ -97,10 +97,10 @@ declareExtension('amp-install-serviceworker', '0.1', false);
 declareExtension('amp-izlesene', '0.1', false);
 declareExtension('amp-jwplayer', '0.1', false, 'NO_TYPE_CHECK');
 declareExtension('amp-lightbox', '0.1', true);
-declareExtension('amp-lightbox-viewer', '0.1', true, 'NO_TYPE_CHECK');
-declareExtension('amp-list', '0.1', false, 'NO_TYPE_CHECK');
+declareExtension('amp-lightbox-viewer', '0.1', true);
+declareExtension('amp-list', '0.1', false);
 declareExtension('amp-live-list', '0.1', true);
-declareExtension('amp-mustache', '0.1', false, 'NO_TYPE_CHECK');
+declareExtension('amp-mustache', '0.1', false);
 declareExtension('amp-nexxtv-player', '0.1', false);
 declareExtension('amp-o2-player', '0.1', false, 'NO_TYPE_CHECK');
 declareExtension('amp-ooyala-player', '0.1', false);
@@ -128,7 +128,7 @@ declareExtension('amp-user-notification', '0.1', true);
 declareExtension('amp-vimeo', '0.1', false, 'NO_TYPE_CHECK');
 declareExtension('amp-vine', '0.1', false, 'NO_TYPE_CHECK');
 declareExtension('amp-viz-vega', '0.1', true);
-declareExtension('amp-google-vrview-image', '0.1', false, 'NO_TYPE_CHECK');
+declareExtension('amp-google-vrview-image', '0.1', false);
 declareExtension('amp-viewer-integration', '0.1', {
   // The viewer integration code needs to run asap, so that viewers
   // can influence document state asap. Otherwise the document may take
diff --git a/src/dom.js b/src/dom.js
index 00228ce53914..4d673550336b 100644
--- a/src/dom.js
+++ b/src/dom.js
@@ -294,7 +294,7 @@ export function matches(el, selector) {
 
 /**
  * Finds the first descendant element with the specified name.
- * @param {!Element} element
+ * @param {!Element|!Document|!ShadowRoot} element
  * @param {string} tagName
  * @return {?Element}
  */
diff --git a/src/services.js b/src/services.js
index 4adb48e64e3f..3718ab563cb0 100644
--- a/src/services.js
+++ b/src/services.js
@@ -228,12 +228,12 @@ export function urlReplacementsForDoc(nodeOrDoc) {
 
 /**
  * @param {!Window} window
- * @return {!Promise<!UserNotificationManager>}
+ * @return {!Promise<!../extensions/amp-user-notification/0.1/amp-user-notification.UserNotificationManager>}
  */
 export function userNotificationManagerFor(window) {
-  return /** @type {!Promise<!UserNotificationManager>} */ (
-      getElementService(window, 'userNotificationManager',
-          'amp-user-notification'));
+  return (/** @type {!Promise<!../extensions/amp-user-notification/0.1/amp-user-notification.UserNotificationManager>} */
+      (getElementService(window, 'userNotificationManager',
+          'amp-user-notification')));
 }
 
 /**