diff --git a/.travis.yml b/.travis.yml
index 647451c1326..9675ab1ab36 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,31 +4,10 @@ language: php
 # Opt to use Travis container-based environment.
 sudo: false
 
-# PHP version used in first build configuration.
-php:
-    - "7.1"
-
-# WordPress version used in first build configuration.
-env:
-    - WP_VERSION=latest
-
 # Newer versions like trusty don't have PHP 5.2 or 5.3
 # https://blog.travis-ci.com/2017-07-11-trusty-as-default-linux-is-coming
 dist: precise
 
-# Next we define our matrix of additional build configurations to test against.
-# The versions listed above will automatically create our first configuration,
-# so it doesn't need to be re-defined below.
-
-# WP_VERSION specifies the tag to use. The way these tests are configured to run
-# requires at least WordPress 3.8. Specify "latest" to test against SVN trunk.
-
-# Note that Travis CI supports listing these above to automatically build a
-# matrix of configurations, but we're being nice here by manually building a
-# total of four configurations even though we're testing 4 versions of PHP
-# along with 2 versions of WordPress (which would build 8 configs otherwise).
-# This takes half as long to run while still providing adequate coverage.
-
 notifications:
   email:
     on_success: never
@@ -44,19 +23,20 @@ matrix:
   include:
    - php: "5.3"
      env: WP_VERSION=latest DEV_LIB_SKIP=composer,phpcs
-   - php: "5.3"
-     env: WP_VERSION=4.7 DEV_LIB_SKIP=composer,phpcs
    - php: "5.4"
-     env: WP_VERSION=latest
-   - php: "5.4"
-     env: WP_VERSION=4.7
-   - php: "7.0"
-     env: WP_VERSION=latest
+     env: WP_VERSION=4.7    DEV_LIB_SKIP=composer,phpcs
+   - php: "5.5"
+     env: WP_VERSION=latest DEV_LIB_SKIP=phpcs
+   - php: "5.6"
+     env: WP_VERSION=4.8    DEV_LIB_SKIP=phpcs
+   - php: "5.6"
+     env: WP_VERSION=latest DEV_LIB_SKIP=phpcs
    - php: "7.0"
-     env: WP_VERSION=4.7
-     # 7.1 / latest already included above as first build.
+     env: WP_VERSION=latest DEV_LIB_SKIP=phpcs
    - php: "7.1"
-     env: WP_VERSION=4.7
+     env: WP_VERSION=latest DEV_LIB_SKIP=phpcs
+   - php: "7.2"
+     env: WP_VERSION=trunk
 
 install:
   - if [[ $DEV_LIB_SKIP =~ composer ]]; then composer install --no-dev; fi
diff --git a/includes/amp-frontend-actions.php b/includes/amp-frontend-actions.php
index f62b93f6b70..f5d7ebca13d 100644
--- a/includes/amp-frontend-actions.php
+++ b/includes/amp-frontend-actions.php
@@ -10,23 +10,31 @@
 /**
  * Add amphtml link to frontend.
  *
+ * @todo This function's name is incorrect. It's not about adding a canonical link but adding the amphtml link.
+ *
  * @since 0.2
  */
 function amp_frontend_add_canonical() {
 
-	// Prevent showing amphtml link if theme supports AMP but paired mode is not available.
-	if ( current_theme_supports( 'amp' ) && ! AMP_Theme_Support::is_paired_available() ) {
-		return;
-	}
-
 	/**
 	 * Filters whether to show the amphtml link on the frontend.
 	 *
+	 * @todo This filter's name is incorrect. It's not about adding a canonical link but adding the amphtml link.
 	 * @since 0.2
 	 */
 	if ( false === apply_filters( 'amp_frontend_show_canonical', true ) ) {
 		return;
 	}
 
-	printf( '<link rel="amphtml" href="%s">', esc_url( amp_get_permalink( get_queried_object_id() ) ) );
+	$amp_url = null;
+	if ( is_singular() ) {
+		$amp_url = amp_get_permalink( get_queried_object_id() );
+	} elseif ( isset( $_SERVER['REQUEST_URI'] ) ) {
+		$host_url = preg_replace( '#(^https?://[^/]+)/.*#', '$1', home_url( '/' ) );
+		$self_url = esc_url_raw( $host_url . wp_unslash( $_SERVER['REQUEST_URI'] ) );
+		$amp_url  = add_query_arg( amp_get_slug(), '', $self_url );
+	}
+	if ( $amp_url ) {
+		printf( '<link rel="amphtml" href="%s">', esc_url( $amp_url ) );
+	}
 }
diff --git a/includes/class-amp-theme-support.php b/includes/class-amp-theme-support.php
index 59d08e5a6d4..01207b645ca 100644
--- a/includes/class-amp-theme-support.php
+++ b/includes/class-amp-theme-support.php
@@ -89,7 +89,6 @@ public static function init() {
 
 		self::purge_amp_query_vars();
 		self::handle_xhr_request();
-		self::add_temporary_discussion_restrictions();
 
 		require_once AMP__DIR__ . '/includes/amp-post-template-actions.php';
 
@@ -121,7 +120,13 @@ public static function init() {
 	 */
 	public static function finish_init() {
 		if ( ! is_amp_endpoint() ) {
-			amp_add_frontend_actions();
+			// Add amphtml link when paired mode is available.
+			if ( self::is_paired_available() ) {
+				amp_add_frontend_actions(); // @todo This function is poor in how it requires a file that then does add_action().
+				if ( ! has_action( 'wp_head', 'amp_frontend_add_canonical' ) ) {
+					add_action( 'wp_head', 'amp_frontend_add_canonical' );
+				}
+			}
 			return;
 		}
 
@@ -228,9 +233,7 @@ public static function add_hooks() {
 		add_action( 'wp_head', 'amp_add_generator_metadata', 20 );
 
 		add_action( 'wp_enqueue_scripts', array( __CLASS__, 'enqueue_assets' ) );
-		if ( is_customize_preview() ) {
-			add_action( 'wp_enqueue_scripts', array( __CLASS__, 'dequeue_customize_preview_scripts' ), 1000 );
-		}
+		add_action( 'wp_enqueue_scripts', array( __CLASS__, 'dequeue_customize_preview_scripts' ), 1000 );
 		add_filter( 'customize_partial_render', array( __CLASS__, 'filter_customize_partial_render' ) );
 
 		add_action( 'wp_footer', 'amp_print_analytics' );
@@ -248,12 +251,13 @@ public static function add_hooks() {
 		add_action( 'template_redirect', array( __CLASS__, 'start_output_buffering' ), 0 );
 
 		// Commenting hooks.
-		add_filter( 'wp_list_comments_args', array( __CLASS__, 'amp_set_comments_walker' ), PHP_INT_MAX );
+		add_filter( 'wp_list_comments_args', array( __CLASS__, 'set_comments_walker' ), PHP_INT_MAX );
 		add_filter( 'comment_form_defaults', array( __CLASS__, 'filter_comment_form_defaults' ) );
 		add_filter( 'comment_reply_link', array( __CLASS__, 'filter_comment_reply_link' ), 10, 4 );
 		add_filter( 'cancel_comment_reply_link', array( __CLASS__, 'filter_cancel_comment_reply_link' ), 10, 3 );
 		add_action( 'comment_form', array( __CLASS__, 'amend_comment_form' ), 100 );
 		remove_action( 'comment_form', 'wp_comment_form_unfiltered_html_nonce' );
+		add_filter( 'wp_kses_allowed_html', array( __CLASS__, 'whitelist_layout_in_wp_kses_allowed_html' ), 10 );
 
 		if ( AMP_Validation_Utils::should_validate_response() ) {
 			AMP_Validation_Utils::add_validation_hooks();
@@ -496,35 +500,6 @@ public static function intercept_post_request_redirect( $location ) {
 		wp_send_json_success();
 	}
 
-	/**
-	 * Set up some restrictions for commenting based on amp-live-list limitations.
-	 *
-	 * Temporarily force comments to be listed in descending order.
-	 * The following hooks are temporary while waiting for amphtml#5396 to be resolved.
-	 *
-	 * @link https://github.com/ampproject/amphtml/issues/5396
-	 */
-	protected static function add_temporary_discussion_restrictions() {
-		add_filter( 'option_comment_order', function() {
-			return 'desc';
-		}, PHP_INT_MAX );
-
-		add_action( 'admin_print_footer_scripts-options-discussion.php', function() {
-			?>
-			<div class="notice notice-info inline" id="amp-comment-notice"><p><?php echo wp_kses_post( __( 'Note: AMP does not yet <a href="https://github.com/ampproject/amphtml/issues/5396" target="_blank">support ascending</a> comments with newer entries appearing at the bottom.', 'amp' ) ); ?></p></div>
-			<script>
-			// Move the notice below the selector and disable selector.
-			jQuery( function( $ ) {
-				var orderSelect = $( '#comment_order' ),
-					notice = $( '#amp-comment-notice' );
-				orderSelect.prop( 'disabled', true );
-				orderSelect.closest( 'fieldset' ).append( notice );
-			} );
-			</script>
-			<?php
-		} );
-	}
-
 	/**
 	 * Register/override widgets.
 	 *
@@ -595,12 +570,9 @@ public static function register_content_embed_handlers() {
 	 * @param array $args the args for the comments list..
 	 * @return array Args to return.
 	 */
-	public static function amp_set_comments_walker( $args ) {
+	public static function set_comments_walker( $args ) {
 		$amp_walker     = new AMP_Comment_Walker();
 		$args['walker'] = $amp_walker;
-		// Add reverse order here as well, in case theme overrides it.
-		$args['reverse_top_level'] = true;
-
 		return $args;
 	}
 
@@ -942,12 +914,12 @@ public static function dequeue_customize_preview_scripts() {
 	public static function start_output_buffering() {
 		/*
 		 * Disable the New Relic Browser agent on AMP responses.
-		 * This prevents th New Relic from causing invalid AMP responses due the NREUM script it injects after the meta charset:
+		 * This prevents the New Relic from causing invalid AMP responses due the NREUM script it injects after the meta charset:
 		 * https://docs.newrelic.com/docs/browser/new-relic-browser/troubleshooting/google-amp-validator-fails-due-3rd-party-script
 		 * Sites with New Relic will need to specially configure New Relic for AMP:
 		 * https://docs.newrelic.com/docs/browser/new-relic-browser/installation/monitor-amp-pages-new-relic-browser
 		 */
-		if ( extension_loaded( 'newrelic' ) ) {
+		if ( function_exists( 'newrelic_disable_autorum' ) ) {
 			newrelic_disable_autorum();
 		}
 
@@ -1120,6 +1092,22 @@ public static function prepare_response( $response, $args = array() ) {
 		return $response;
 	}
 
+	/**
+	 * Adds 'data-amp-layout' to the allowed <img> attributes for wp_kses().
+	 *
+	 * @since 0.7
+	 *
+	 * @param array $context Allowed tags and their allowed attributes.
+	 * @return array $context Filtered allowed tags and attributes.
+	 */
+	public static function whitelist_layout_in_wp_kses_allowed_html( $context ) {
+		if ( ! empty( $context['img']['width'] ) && ! empty( $context['img']['height'] ) ) {
+			$context['img']['data-amp-layout'] = true;
+		}
+
+		return $context;
+	}
+
 	/**
 	 * Enqueue AMP assets if this is an AMP endpoint.
 	 *
diff --git a/includes/sanitizers/class-amp-allowed-tags-generated.php b/includes/sanitizers/class-amp-allowed-tags-generated.php
index c7d8f0c357a..f666c891ae0 100644
--- a/includes/sanitizers/class-amp-allowed-tags-generated.php
+++ b/includes/sanitizers/class-amp-allowed-tags-generated.php
@@ -13,8 +13,8 @@
  */
 class AMP_Allowed_Tags_Generated {
 
-	private static $spec_file_revision = 566;
-	private static $minimum_validator_revision_required = 314;
+	private static $spec_file_revision = 595;
+	private static $minimum_validator_revision_required = 322;
 
 	private static $allowed_tags = array(
 		'a' => array(
@@ -34,6 +34,7 @@ class AMP_Allowed_Tags_Generated {
 								'http',
 								'https',
 								'mailto',
+								'maps',
 								'bbmi',
 								'fb-messenger',
 								'intent',
@@ -53,6 +54,7 @@ class AMP_Allowed_Tags_Generated {
 					'hreflang' => array(),
 					'media' => array(),
 					'name' => array(),
+					'referrerpolicy' => array(),
 					'rel' => array(
 						'blacklisted_value_regex' => '(^|\\s)(components|dns-prefetch|import|manifest|preconnect|prefetch|preload|prerender|serviceworker|stylesheet|subresource|)(\\s|$)',
 					),
@@ -115,6 +117,9 @@ class AMP_Allowed_Tags_Generated {
 					'disable-session-states' => array(
 						'value' => '',
 					),
+					'expand-single-section' => array(
+						'value' => '',
+					),
 				),
 				'tag_spec' => array(
 					'requires_extension' => array(
@@ -143,6 +148,7 @@ class AMP_Allowed_Tags_Generated {
 							),
 						),
 					),
+					'template' => array(),
 					'type' => array(
 						'mandatory' => true,
 					),
@@ -471,6 +477,32 @@ class AMP_Allowed_Tags_Generated {
 				),
 			),
 		),
+		'amp-beopinion' => array(
+			array(
+				'attr_spec_list' => array(
+					'data-account' => array(
+						'mandatory' => true,
+						'value_regex_casei' => '[0-9a-f]{24}',
+					),
+					'data-content' => array(
+						'value_regex_casei' => '[0-9a-f]{24}',
+					),
+					'data-my-content' => array(
+						'value_regex' => '0|1',
+					),
+					'data-name' => array(),
+					'media' => array(),
+					'noloading' => array(
+						'value' => '',
+					),
+				),
+				'tag_spec' => array(
+					'requires_extension' => array(
+						'amp-beopinion',
+					),
+				),
+			),
+		),
 		'amp-bind-macro' => array(
 			array(
 				'attr_spec_list' => array(
@@ -490,6 +522,33 @@ class AMP_Allowed_Tags_Generated {
 				),
 			),
 		),
+		'amp-bodymovin-animation' => array(
+			array(
+				'attr_spec_list' => array(
+					'loop' => array(
+						'value_regex_casei' => '(false|number|true)',
+					),
+					'noautoplay' => array(
+						'value' => '',
+					),
+					'src' => array(
+						'mandatory' => true,
+						'value_url' => array(
+							'allow_relative' => false,
+							'allowed_protocol' => array(
+								'https',
+							),
+						),
+					),
+				),
+				'tag_spec' => array(
+					'requires_extension' => array(
+						'amp-bodymovin-animation',
+					),
+					'spec_url' => 'https://www.ampproject.org/docs/reference/components/amp-bodymovin-animation',
+				),
+			),
+		),
 		'amp-brid-player' => array(
 			array(
 				'attr_spec_list' => array(
@@ -613,6 +672,13 @@ class AMP_Allowed_Tags_Generated {
 					'dots' => array(
 						'value' => '',
 					),
+					'lightbox' => array(),
+					'lightbox-exclude' => array(
+						'value' => '',
+					),
+					'lightbox-thumbnail-id' => array(
+						'value_regex_casei' => '^[a-z][a-z\\d_-]*',
+					),
 					'loop' => array(
 						'value' => '',
 					),
@@ -632,6 +698,22 @@ class AMP_Allowed_Tags_Generated {
 				),
 			),
 		),
+		'amp-consent' => array(
+			array(
+				'attr_spec_list' => array(
+					'media' => array(),
+					'noloading' => array(
+						'value' => '',
+					),
+				),
+				'tag_spec' => array(
+					'requires_extension' => array(
+						'amp-consent',
+					),
+					'unique' => true,
+				),
+			),
+		),
 		'amp-dailymotion' => array(
 			array(
 				'attr_spec_list' => array(
@@ -674,6 +756,256 @@ class AMP_Allowed_Tags_Generated {
 				),
 			),
 		),
+		'amp-date-picker' => array(
+			array(
+				'attr_spec_list' => array(
+					'allow-blocked-ranges' => array(
+						'value' => '',
+					),
+					'blocked' => array(),
+					'day-size' => array(
+						'value_regex' => '[0-9]+',
+					),
+					'first-day-of-week' => array(
+						'value_regex' => '[0-6]',
+					),
+					'format' => array(),
+					'fullscreen' => array(
+						'value' => '',
+					),
+					'highlighted' => array(),
+					'input-selector' => array(),
+					'locale' => array(),
+					'max' => array(),
+					'media' => array(),
+					'min' => array(),
+					'mode' => array(
+						'value_casei' => 'static',
+					),
+					'month-format' => array(),
+					'noloading' => array(
+						'value' => '',
+					),
+					'number-of-months' => array(
+						'value_regex' => '[0-9]+',
+					),
+					'open-after-clear' => array(
+						'value' => '',
+					),
+					'open-after-select' => array(
+						'value' => '',
+					),
+					'src' => array(
+						'blacklisted_value_regex' => '__amp_source_origin',
+						'value_url' => array(
+							'allow_relative' => true,
+							'allowed_protocol' => array(
+								'https',
+							),
+						),
+					),
+					'type' => array(
+						'value_casei' => 'single',
+					),
+					'week-day-format' => array(),
+				),
+				'tag_spec' => array(
+					'requires_extension' => array(
+						'amp-date-picker',
+					),
+					'spec_name' => 'amp-date-picker[type=single][mode=static]',
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'allow-blocked-ranges' => array(
+						'value' => '',
+					),
+					'blocked' => array(),
+					'day-size' => array(
+						'value_regex' => '[0-9]+',
+					),
+					'first-day-of-week' => array(
+						'value_regex' => '[0-6]',
+					),
+					'format' => array(),
+					'highlighted' => array(),
+					'input-selector' => array(),
+					'locale' => array(),
+					'max' => array(),
+					'media' => array(),
+					'min' => array(),
+					'mode' => array(
+						'mandatory' => true,
+						'value_casei' => 'overlay',
+					),
+					'month-format' => array(),
+					'noloading' => array(
+						'value' => '',
+					),
+					'number-of-months' => array(
+						'value_regex' => '[0-9]+',
+					),
+					'open-after-clear' => array(
+						'value' => '',
+					),
+					'open-after-select' => array(
+						'value' => '',
+					),
+					'src' => array(
+						'blacklisted_value_regex' => '__amp_source_origin',
+						'value_url' => array(
+							'allow_relative' => true,
+							'allowed_protocol' => array(
+								'https',
+							),
+						),
+					),
+					'type' => array(
+						'value_casei' => 'single',
+					),
+					'week-day-format' => array(),
+				),
+				'tag_spec' => array(
+					'requires_extension' => array(
+						'amp-date-picker',
+					),
+					'spec_name' => 'amp-date-picker[type=single][mode=overlay]',
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'allow-blocked-ranges' => array(
+						'value' => '',
+					),
+					'blocked' => array(),
+					'day-size' => array(
+						'value_regex' => '[0-9]+',
+					),
+					'end-input-selector' => array(),
+					'first-day-of-week' => array(
+						'value_regex' => '[0-6]',
+					),
+					'format' => array(),
+					'fullscreen' => array(
+						'value' => '',
+					),
+					'highlighted' => array(),
+					'locale' => array(),
+					'max' => array(),
+					'media' => array(),
+					'min' => array(),
+					'mode' => array(
+						'value_casei' => 'static',
+					),
+					'month-format' => array(),
+					'noloading' => array(
+						'value' => '',
+					),
+					'number-of-months' => array(
+						'value_regex' => '[0-9]+',
+					),
+					'open-after-clear' => array(
+						'value' => '',
+					),
+					'open-after-select' => array(
+						'value' => '',
+					),
+					'src' => array(
+						'blacklisted_value_regex' => '__amp_source_origin',
+						'value_url' => array(
+							'allow_relative' => true,
+							'allowed_protocol' => array(
+								'https',
+							),
+						),
+					),
+					'start-input-selector' => array(),
+					'type' => array(
+						'mandatory' => true,
+						'value_casei' => 'range',
+					),
+					'week-day-format' => array(),
+				),
+				'tag_spec' => array(
+					'requires_extension' => array(
+						'amp-date-picker',
+					),
+					'spec_name' => 'amp-date-picker[type=range][mode=static]',
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'allow-blocked-ranges' => array(
+						'value' => '',
+					),
+					'blocked' => array(),
+					'day-size' => array(
+						'value_regex' => '[0-9]+',
+					),
+					'end-input-selector' => array(),
+					'first-day-of-week' => array(
+						'value_regex' => '[0-6]',
+					),
+					'format' => array(),
+					'highlighted' => array(),
+					'locale' => array(),
+					'max' => array(),
+					'media' => array(),
+					'min' => array(),
+					'mode' => array(
+						'mandatory' => true,
+						'value_casei' => 'overlay',
+					),
+					'month-format' => array(),
+					'noloading' => array(
+						'value' => '',
+					),
+					'number-of-months' => array(
+						'value_regex' => '[0-9]+',
+					),
+					'open-after-clear' => array(
+						'value' => '',
+					),
+					'open-after-select' => array(
+						'value' => '',
+					),
+					'src' => array(
+						'blacklisted_value_regex' => '__amp_source_origin',
+						'value_url' => array(
+							'allow_relative' => true,
+							'allowed_protocol' => array(
+								'https',
+							),
+						),
+					),
+					'start-input-selector' => array(),
+					'type' => array(
+						'mandatory' => true,
+						'value_casei' => 'range',
+					),
+					'week-day-format' => array(),
+				),
+				'tag_spec' => array(
+					'requires_extension' => array(
+						'amp-date-picker',
+					),
+					'spec_name' => 'amp-date-picker[type=range][mode=overlay]',
+				),
+			),
+		),
+		'amp-document-recommendations' => array(
+			array(
+				'attr_spec_list' => array(),
+				'tag_spec' => array(
+					'mandatory_parent' => 'body',
+					'requires_extension' => array(
+						'amp-document-recommendations',
+					),
+					'spec_url' => 'https://www.ampproject.org/docs/reference/components/amp-document-recommendations',
+				),
+			),
+		),
 		'amp-embed' => array(
 			array(
 				'attr_spec_list' => array(
@@ -693,6 +1025,7 @@ class AMP_Allowed_Tags_Generated {
 							),
 						),
 					),
+					'template' => array(),
 					'type' => array(
 						'mandatory' => true,
 					),
@@ -1028,6 +1361,9 @@ class AMP_Allowed_Tags_Generated {
 		'amp-ima-video' => array(
 			array(
 				'attr_spec_list' => array(
+					'autoplay' => array(
+						'value' => '',
+					),
 					'data-src' => array(
 						'blacklisted_value_regex' => '__amp_source_origin',
 						'value_url' => array(
@@ -1084,6 +1420,13 @@ class AMP_Allowed_Tags_Generated {
 					'[srcset]' => array(),
 					'alt' => array(),
 					'attribution' => array(),
+					'lightbox' => array(),
+					'lightbox-exclude' => array(
+						'value' => '',
+					),
+					'lightbox-thumbnail-id' => array(
+						'value_regex_casei' => '^[a-z][a-z\\d_-]*',
+					),
 					'media' => array(),
 					'noloading' => array(
 						'value' => '',
@@ -1278,6 +1621,9 @@ class AMP_Allowed_Tags_Generated {
 					'noloading' => array(
 						'value' => '',
 					),
+					'reset-on-refresh' => array(
+						'value' => '',
+					),
 					'single-item' => array(),
 					'src' => array(
 						'blacklisted_value_regex' => '__amp_source_origin',
@@ -1297,6 +1643,37 @@ class AMP_Allowed_Tags_Generated {
 					),
 				),
 			),
+			array(
+				'attr_spec_list' => array(
+					'[src]' => array(
+						'mandatory' => true,
+					),
+					'credentials' => array(),
+					'items' => array(),
+					'max-items' => array(),
+					'media' => array(),
+					'noloading' => array(
+						'value' => '',
+					),
+					'single-item' => array(),
+					'src' => array(
+						'blacklisted_value_regex' => '__amp_source_origin',
+						'value_url' => array(
+							'allow_relative' => true,
+							'allowed_protocol' => array(
+								'https',
+							),
+						),
+					),
+					'template' => array(),
+				),
+				'tag_spec' => array(
+					'requires_extension' => array(
+						'amp-list',
+					),
+					'spec_name' => 'AMP-LIST [SRC]',
+				),
+			),
 		),
 		'amp-live-list' => array(
 			array(
@@ -1314,6 +1691,9 @@ class AMP_Allowed_Tags_Generated {
 					'id' => array(
 						'mandatory' => true,
 					),
+					'sort' => array(
+						'value_regex' => 'ascending',
+					),
 				),
 				'tag_spec' => array(
 					'requires_extension' => array(
@@ -1825,6 +2205,27 @@ class AMP_Allowed_Tags_Generated {
 				),
 			),
 		),
+		'amp-story-auto-ads' => array(
+			array(
+				'attr_spec_list' => array(),
+				'tag_spec' => array(
+					'mandatory_parent' => 'amp-story',
+					'requires_extension' => array(
+						'amp-story-auto-ads',
+					),
+					'spec_url' => 'https://github.com/ampproject/amphtml/blob/master/extensions/amp-story/amp-story-auto-ads.md',
+					'unique' => true,
+				),
+			),
+		),
+		'amp-story-cta-layer' => array(
+			array(
+				'attr_spec_list' => array(),
+				'tag_spec' => array(
+					'mandatory_ancestor' => 'amp-story-page',
+				),
+			),
+		),
 		'amp-story-grid-layer' => array(
 			array(
 				'attr_spec_list' => array(
@@ -1971,6 +2372,13 @@ class AMP_Allowed_Tags_Generated {
 					'disableremoteplayback' => array(
 						'value' => '',
 					),
+					'lightbox' => array(),
+					'lightbox-exclude' => array(
+						'value' => '',
+					),
+					'lightbox-thumbnail-id' => array(
+						'value_regex_casei' => '^[a-z][a-z\\d_-]*',
+					),
 					'loop' => array(
 						'value' => '',
 					),
@@ -2228,6 +2636,13 @@ class AMP_Allowed_Tags_Generated {
 					'data-videoid' => array(
 						'value_regex' => '[^=/?:]+',
 					),
+					'lightbox' => array(),
+					'lightbox-exclude' => array(
+						'value' => '',
+					),
+					'lightbox-thumbnail-id' => array(
+						'value_regex_casei' => '^[a-z][a-z\\d_-]*',
+					),
 					'media' => array(),
 					'noloading' => array(
 						'value' => '',
@@ -4684,7 +5099,7 @@ class AMP_Allowed_Tags_Generated {
 					'hreflang' => array(),
 					'media' => array(),
 					'rel' => array(
-						'blacklisted_value_regex' => '(^|\\s)(canonical|components|import|manifest|serviceworker|stylesheet|subresource|)(\\s|$)',
+						'blacklisted_value_regex' => '(^|\\s)(canonical|components|import|manifest|preload|serviceworker|stylesheet|subresource|)(\\s|$)',
 						'mandatory' => true,
 					),
 					'sizes' => array(),
@@ -4770,13 +5185,41 @@ class AMP_Allowed_Tags_Generated {
 					'spec_url' => 'https://www.ampproject.org/docs/reference/spec#html-tags',
 				),
 			),
+			array(
+				'attr_spec_list' => array(
+					'as' => array(),
+					'charset' => array(
+						'value_casei' => 'utf-8',
+					),
+					'color' => array(),
+					'crossorigin' => array(),
+					'href' => array(),
+					'hreflang' => array(),
+					'media' => array(),
+					'rel' => array(
+						'dispatch_key' => 2,
+						'mandatory' => true,
+						'value_casei' => 'preload',
+					),
+					'sizes' => array(),
+					'target' => array(),
+					'type' => array(),
+				),
+				'tag_spec' => array(
+					'disallowed_ancestor' => array(
+						'template',
+					),
+					'spec_name' => 'link rel=preload',
+					'spec_url' => 'https://www.ampproject.org/docs/reference/spec#html-tags',
+				),
+			),
 			array(
 				'attr_spec_list' => array(
 					'async' => array(),
 					'crossorigin' => array(),
 					'href' => array(
 						'mandatory' => true,
-						'value_regex' => 'https://cdn\\.materialdesignicons\\.com/([0-9]+\\.?)+/css/materialdesignicons\\.min\\.css|https://cloud\\.typography\\.com/[0-9]*/[0-9]*/css/fonts\\.css|https://fast\\.fonts\\.net/.*|https://fonts\\.googleapis\\.com/css\\?.*|https://fonts\\.googleapis\\.com/icon\\?.*|https://fonts\\.googleapis\\.com/earlyaccess/.*\\.css|https://maxcdn\\.bootstrapcdn\\.com/font-awesome/([0-9]+\\.?)+/css/font-awesome\\.min\\.css(\\?.*)?|https://use\\.typekit\\.net/[\\w\\p{L}\\p{N}_]+\\.css',
+						'value_regex' => 'https://cdn\\.materialdesignicons\\.com/([0-9]+\\.?)+/css/materialdesignicons\\.min\\.css|https://cloud\\.typography\\.com/[0-9]*/[0-9]*/css/fonts\\.css|https://fast\\.fonts\\.net/.*|https://fonts\\.googleapis\\.com/css\\?.*|https://fonts\\.googleapis\\.com/icon\\?.*|https://fonts\\.googleapis\\.com/earlyaccess/.*\\.css|https://maxcdn\\.bootstrapcdn\\.com/font-awesome/([0-9]+\\.?)+/css/font-awesome\\.min\\.css(\\?.*)?|https://use\\.fontawesome\\.com/releases/v([0-9]+\\.?)+/css/(all|brands|solids|fontawesome)\\.css|https://use\\.typekit\\.net/[\\w\\p{L}\\p{N}_]+\\.css',
 					),
 					'integrity' => array(),
 					'media' => array(),
@@ -5264,6 +5707,7 @@ class AMP_Allowed_Tags_Generated {
 						'blacklisted_value_regex' => '(^|\\s)(amp-.*|amp4ads-.*|apple-itunes-app|content-disposition|revisit-after|viewport)(\\s|$)',
 					),
 					'property' => array(),
+					'scheme' => array(),
 				),
 				'tag_spec' => array(
 					'spec_name' => 'meta name= and content=',
@@ -5408,6 +5852,24 @@ class AMP_Allowed_Tags_Generated {
 					'spec_url' => 'https://www.ampproject.org/docs/reference/spec#html-tags',
 				),
 			),
+			array(
+				'attr_spec_list' => array(
+					'content' => array(
+						'mandatory' => true,
+						'value_regex_casei' => '(off|on)',
+					),
+					'http-equiv' => array(
+						'dispatch_key' => 2,
+						'mandatory' => true,
+						'value_casei' => 'x-dns-prefetch-control',
+					),
+				),
+				'tag_spec' => array(
+					'mandatory_ancestor' => 'head',
+					'spec_name' => 'meta http-equiv=x-dns-prefetch-control',
+					'spec_url' => 'https://www.ampproject.org/docs/reference/spec#html-tags',
+				),
+			),
 			array(
 				'attr_spec_list' => array(
 					'content' => array(
@@ -5424,6 +5886,23 @@ class AMP_Allowed_Tags_Generated {
 					'spec_name' => 'meta name=amp-ad-enable-refresh',
 				),
 			),
+			array(
+				'attr_spec_list' => array(
+					'content' => array(
+						'mandatory' => true,
+					),
+					'name' => array(
+						'dispatch_key' => 2,
+						'mandatory' => true,
+						'value_casei' => 'amp-to-amp-navigation',
+					),
+				),
+				'tag_spec' => array(
+					'mandatory_parent' => 'head',
+					'spec_name' => 'meta name=amp-to-amp-navigation',
+					'unique' => true,
+				),
+			),
 		),
 		'metadata' => array(
 			array(
@@ -6571,7 +7050,162 @@ class AMP_Allowed_Tags_Generated {
 							'0.1',
 							'latest',
 						),
-						'name' => 'amp-animation',
+						'name' => 'amp-animation',
+					),
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'nonce' => array(),
+					'type' => array(
+						'dispatch_key' => 3,
+						'mandatory' => true,
+						'value_casei' => 'application/json',
+					),
+				),
+				'cdata' => array(
+					'blacklisted_cdata_regex' => array(
+						'error_message' => 'html comments',
+						'regex' => '<!--',
+					),
+				),
+				'tag_spec' => array(
+					'mandatory_parent' => 'amp-animation',
+					'requires_extension' => array(
+						'amp-animation',
+					),
+					'spec_name' => 'amp-animation extension .json script',
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'async' => array(
+						'mandatory' => true,
+						'value' => '',
+					),
+					'nonce' => array(),
+					'type' => array(
+						'value_casei' => 'text/javascript',
+					),
+				),
+				'tag_spec' => array(
+					'extension_spec' => array(
+						'allowed_versions' => array(
+							'0.1',
+							'latest',
+						),
+						'deprecated_allow_duplicates' => true,
+						'name' => 'amp-apester-media',
+						'requires_usage' => 2,
+					),
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'async' => array(
+						'mandatory' => true,
+						'value' => '',
+					),
+					'nonce' => array(),
+					'type' => array(
+						'value_casei' => 'text/javascript',
+					),
+				),
+				'tag_spec' => array(
+					'extension_spec' => array(
+						'allowed_versions' => array(
+							'0.1',
+							'latest',
+						),
+						'deprecated_allow_duplicates' => true,
+						'name' => 'amp-app-banner',
+					),
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'async' => array(
+						'mandatory' => true,
+						'value' => '',
+					),
+					'nonce' => array(),
+					'type' => array(
+						'value_casei' => 'text/javascript',
+					),
+				),
+				'tag_spec' => array(
+					'extension_spec' => array(
+						'allowed_versions' => array(
+							'0.1',
+							'latest',
+						),
+						'deprecated_allow_duplicates' => true,
+						'name' => 'amp-audio',
+						'requires_usage' => 2,
+					),
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'async' => array(
+						'mandatory' => true,
+						'value' => '',
+					),
+					'nonce' => array(),
+					'type' => array(
+						'value_casei' => 'text/javascript',
+					),
+				),
+				'tag_spec' => array(
+					'extension_spec' => array(
+						'allowed_versions' => array(
+							'0.1',
+							'latest',
+						),
+						'name' => 'amp-auto-ads',
+					),
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'async' => array(
+						'mandatory' => true,
+						'value' => '',
+					),
+					'nonce' => array(),
+					'type' => array(
+						'value_casei' => 'text/javascript',
+					),
+				),
+				'tag_spec' => array(
+					'extension_spec' => array(
+						'allowed_versions' => array(
+							'0.1',
+							'latest',
+						),
+						'name' => 'amp-beopinion',
+					),
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'async' => array(
+						'mandatory' => true,
+						'value' => '',
+					),
+					'nonce' => array(),
+					'type' => array(
+						'value_casei' => 'text/javascript',
+					),
+				),
+				'tag_spec' => array(
+					'extension_spec' => array(
+						'allowed_versions' => array(
+							'0.1',
+							'latest',
+						),
+						'name' => 'amp-bind',
+						'requires_usage' => 3,
 					),
 				),
 			),
@@ -6591,11 +7225,12 @@ class AMP_Allowed_Tags_Generated {
 					),
 				),
 				'tag_spec' => array(
-					'mandatory_parent' => 'amp-animation',
+					'mandatory_parent' => 'amp-state',
 					'requires_extension' => array(
-						'amp-animation',
+						'amp-bind',
 					),
-					'spec_name' => 'amp-animation extension .json script',
+					'spec_name' => 'amp-bind extension .json script',
+					'spec_url' => 'https://www.ampproject.org/docs/reference/components/amp-bind',
 				),
 			),
 			array(
@@ -6615,9 +7250,7 @@ class AMP_Allowed_Tags_Generated {
 							'0.1',
 							'latest',
 						),
-						'deprecated_allow_duplicates' => true,
-						'name' => 'amp-apester-media',
-						'requires_usage' => 2,
+						'name' => 'amp-bodymovin-animation',
 					),
 				),
 			),
@@ -6639,7 +7272,8 @@ class AMP_Allowed_Tags_Generated {
 							'latest',
 						),
 						'deprecated_allow_duplicates' => true,
-						'name' => 'amp-app-banner',
+						'name' => 'amp-brid-player',
+						'requires_usage' => 2,
 					),
 				),
 			),
@@ -6661,7 +7295,7 @@ class AMP_Allowed_Tags_Generated {
 							'latest',
 						),
 						'deprecated_allow_duplicates' => true,
-						'name' => 'amp-audio',
+						'name' => 'amp-brightcove',
 						'requires_usage' => 2,
 					),
 				),
@@ -6683,7 +7317,7 @@ class AMP_Allowed_Tags_Generated {
 							'0.1',
 							'latest',
 						),
-						'name' => 'amp-auto-ads',
+						'name' => 'amp-byside-content',
 					),
 				),
 			),
@@ -6704,33 +7338,9 @@ class AMP_Allowed_Tags_Generated {
 							'0.1',
 							'latest',
 						),
-						'name' => 'amp-bind',
-						'requires_usage' => 3,
-					),
-				),
-			),
-			array(
-				'attr_spec_list' => array(
-					'nonce' => array(),
-					'type' => array(
-						'dispatch_key' => 3,
-						'mandatory' => true,
-						'value_casei' => 'application/json',
-					),
-				),
-				'cdata' => array(
-					'blacklisted_cdata_regex' => array(
-						'error_message' => 'html comments',
-						'regex' => '<!--',
-					),
-				),
-				'tag_spec' => array(
-					'mandatory_parent' => 'amp-state',
-					'requires_extension' => array(
-						'amp-bind',
+						'name' => 'amp-call-tracking',
+						'requires_usage' => 2,
 					),
-					'spec_name' => 'amp-bind extension .json script',
-					'spec_url' => 'https://www.ampproject.org/docs/reference/components/amp-bind',
 				),
 			),
 			array(
@@ -6751,7 +7361,7 @@ class AMP_Allowed_Tags_Generated {
 							'latest',
 						),
 						'deprecated_allow_duplicates' => true,
-						'name' => 'amp-brid-player',
+						'name' => 'amp-carousel',
 						'requires_usage' => 2,
 					),
 				),
@@ -6773,31 +7383,32 @@ class AMP_Allowed_Tags_Generated {
 							'0.1',
 							'latest',
 						),
-						'deprecated_allow_duplicates' => true,
-						'name' => 'amp-brightcove',
-						'requires_usage' => 2,
+						'name' => 'amp-consent',
 					),
 				),
 			),
 			array(
 				'attr_spec_list' => array(
-					'async' => array(
-						'mandatory' => true,
-						'value' => '',
-					),
 					'nonce' => array(),
 					'type' => array(
-						'value_casei' => 'text/javascript',
+						'dispatch_key' => 3,
+						'mandatory' => true,
+						'value_casei' => 'application/json',
+					),
+				),
+				'cdata' => array(
+					'blacklisted_cdata_regex' => array(
+						'error_message' => 'html comments',
+						'regex' => '<!--',
 					),
 				),
 				'tag_spec' => array(
-					'extension_spec' => array(
-						'allowed_versions' => array(
-							'0.1',
-							'latest',
-						),
-						'name' => 'amp-byside-content',
+					'mandatory_parent' => 'amp-consent',
+					'requires_extension' => array(
+						'amp-consent',
 					),
+					'spec_name' => 'amp-consent extension .json script',
+					'unique' => true,
 				),
 			),
 			array(
@@ -6817,7 +7428,8 @@ class AMP_Allowed_Tags_Generated {
 							'0.1',
 							'latest',
 						),
-						'name' => 'amp-call-tracking',
+						'deprecated_allow_duplicates' => true,
+						'name' => 'amp-dailymotion',
 						'requires_usage' => 2,
 					),
 				),
@@ -6839,35 +7451,39 @@ class AMP_Allowed_Tags_Generated {
 							'0.1',
 							'latest',
 						),
-						'deprecated_allow_duplicates' => true,
-						'name' => 'amp-carousel',
-						'requires_usage' => 2,
+						'name' => 'amp-date-picker',
 					),
 				),
 			),
 			array(
-				'attr_spec_list' => array(
-					'async' => array(
-						'mandatory' => true,
-						'value' => '',
-					),
-					'nonce' => array(),
-					'type' => array(
-						'value_casei' => 'text/javascript',
-					),
-				),
+				'attr_spec_list' => array(),
 				'tag_spec' => array(
 					'extension_spec' => array(
 						'allowed_versions' => array(
 							'0.1',
 							'latest',
 						),
-						'deprecated_allow_duplicates' => true,
-						'name' => 'amp-dailymotion',
-						'requires_usage' => 2,
+						'name' => 'amp-document-recommendations',
 					),
 				),
 			),
+			array(
+				'attr_spec_list' => array(
+					'recommendations' => array(
+						'dispatch_key' => 3,
+						'mandatory' => true,
+						'value_casei' => 'application/json',
+					),
+				),
+				'tag_spec' => array(
+					'mandatory_parent' => 'amp-document-recommendations',
+					'requires_extension' => array(
+						'amp-document-recommendations',
+					),
+					'spec_name' => 'amp-document-recommendations extension .json configuration',
+					'spec_url' => 'https://www.ampproject.org/docs/reference/components/amp-document-recommendations',
+				),
+			),
 			array(
 				'attr_spec_list' => array(
 					'async' => array(
@@ -7402,6 +8018,28 @@ class AMP_Allowed_Tags_Generated {
 					),
 				),
 			),
+			array(
+				'attr_spec_list' => array(
+					'async' => array(
+						'mandatory' => true,
+						'value' => '',
+					),
+					'nonce' => array(),
+					'type' => array(
+						'value_casei' => 'text/javascript',
+					),
+				),
+				'tag_spec' => array(
+					'extension_spec' => array(
+						'allowed_versions' => array(
+							'0.1',
+							'latest',
+						),
+						'name' => 'amp-lightbox-gallery',
+						'requires_usage' => 3,
+					),
+				),
+			),
 			array(
 				'attr_spec_list' => array(
 					'async' => array(
@@ -7853,6 +8491,51 @@ class AMP_Allowed_Tags_Generated {
 					),
 				),
 			),
+			array(
+				'attr_spec_list' => array(
+					'async' => array(
+						'mandatory' => true,
+						'value' => '',
+					),
+					'nonce' => array(),
+					'type' => array(
+						'value_casei' => 'text/javascript',
+					),
+				),
+				'tag_spec' => array(
+					'extension_spec' => array(
+						'allowed_versions' => array(
+							'0.1',
+							'latest',
+						),
+						'name' => 'amp-story-auto-ads',
+					),
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'nonce' => array(),
+					'type' => array(
+						'dispatch_key' => 3,
+						'mandatory' => true,
+						'value_casei' => 'application/json',
+					),
+				),
+				'cdata' => array(
+					'blacklisted_cdata_regex' => array(
+						'error_message' => 'html comments',
+						'regex' => '<!--',
+					),
+				),
+				'tag_spec' => array(
+					'mandatory_parent' => 'amp-story-auto-ads',
+					'requires_extension' => array(
+						'amp-story-auto-ads',
+					),
+					'spec_name' => 'amp-story-auto-ads config script',
+					'spec_url' => 'https://github.com/ampproject/amphtml/blob/master/extensions/amp-story/amp-story-auto-ads.md',
+				),
+			),
 			array(
 				'attr_spec_list' => array(
 					'async' => array(
@@ -7874,6 +8557,81 @@ class AMP_Allowed_Tags_Generated {
 					),
 				),
 			),
+			array(
+				'attr_spec_list' => array(
+					'async' => array(
+						'mandatory' => true,
+						'value' => '',
+					),
+					'nonce' => array(),
+					'type' => array(
+						'value_casei' => 'text/javascript',
+					),
+				),
+				'tag_spec' => array(
+					'extension_spec' => array(
+						'allowed_versions' => array(
+							'0.1',
+							'latest',
+						),
+						'name' => 'amp-subscriptions',
+						'requires_usage' => 3,
+					),
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'id' => array(
+						'dispatch_key' => 2,
+						'mandatory' => true,
+						'value' => 'amp-subscriptions',
+					),
+					'nonce' => array(),
+					'type' => array(
+						'mandatory' => true,
+						'value_casei' => 'application/json',
+					),
+				),
+				'cdata' => array(
+					'blacklisted_cdata_regex' => array(
+						'error_message' => 'html comments',
+						'regex' => '<!--',
+					),
+				),
+				'tag_spec' => array(
+					'mandatory_parent' => 'head',
+					'requires_extension' => array(
+						'amp-subscriptions',
+					),
+					'spec_name' => 'amp-subscriptions extension .json script',
+					'unique' => true,
+				),
+			),
+			array(
+				'attr_spec_list' => array(
+					'async' => array(
+						'mandatory' => true,
+						'value' => '',
+					),
+					'nonce' => array(),
+					'type' => array(
+						'value_casei' => 'text/javascript',
+					),
+				),
+				'tag_spec' => array(
+					'extension_spec' => array(
+						'allowed_versions' => array(
+							'0.1',
+							'latest',
+						),
+						'name' => 'amp-subscriptions-google',
+						'requires_usage' => 3,
+					),
+					'requires_extension' => array(
+						'amp-subscriptions',
+					),
+				),
+			),
 			array(
 				'attr_spec_list' => array(
 					'async' => array(
@@ -8847,6 +9605,7 @@ class AMP_Allowed_Tags_Generated {
 				'tag_spec' => array(
 					'disallowed_ancestor' => array(
 						'template',
+						'amp-story-auto-ads',
 						'form > div [submit-success][template]',
 						'form > div [submit-error][template]',
 					),
@@ -8855,6 +9614,21 @@ class AMP_Allowed_Tags_Generated {
 					),
 				),
 			),
+			array(
+				'attr_spec_list' => array(
+					'type' => array(
+						'mandatory' => true,
+						'value' => 'amp-mustache',
+					),
+				),
+				'tag_spec' => array(
+					'mandatory_parent' => 'amp-story-auto-ads',
+					'requires_extension' => array(
+						'amp-mustache',
+					),
+					'spec_name' => 'amp-story-auto-ads > template',
+				),
+			),
 		),
 		'text' => array(
 			array(
@@ -9975,6 +10749,18 @@ class AMP_Allowed_Tags_Generated {
 		'resource' => array(),
 		'rev' => array(),
 		'role' => array(),
+		'subscriptions-action' => array(),
+		'subscriptions-actions' => array(
+			'value' => '',
+		),
+		'subscriptions-dialog' => array(
+			'value' => '',
+		),
+		'subscriptions-display' => array(),
+		'subscriptions-section' => array(
+			'value_regex_casei' => '(actions|content|content-not-granted)',
+		),
+		'subscriptions-service' => array(),
 		'tabindex' => array(),
 		'title' => array(),
 		'translate' => array(),
diff --git a/includes/sanitizers/class-amp-base-sanitizer.php b/includes/sanitizers/class-amp-base-sanitizer.php
index cecf6325ae7..0fc9a697085 100644
--- a/includes/sanitizers/class-amp-base-sanitizer.php
+++ b/includes/sanitizers/class-amp-base-sanitizer.php
@@ -201,7 +201,7 @@ public function sanitize_dimension( $value, $dimension ) {
 	}
 
 	/**
-	 * Enforce fixed height.
+	 * Sets the layout, and possibly the 'height' and 'width' attributes.
 	 *
 	 * @param string[] $attributes {
 	 *      Attributes.
@@ -214,12 +214,11 @@ public function sanitize_dimension( $value, $dimension ) {
 	 * }
 	 * @return string[]
 	 */
-	public function enforce_fixed_height( $attributes ) {
+	public function set_layout( $attributes ) {
 		if ( empty( $attributes['height'] ) ) {
 			unset( $attributes['width'] );
 			$attributes['height'] = self::FALLBACK_HEIGHT;
 		}
-
 		if ( empty( $attributes['width'] ) ) {
 			$attributes['layout'] = 'fixed-height';
 		}
@@ -227,47 +226,6 @@ public function enforce_fixed_height( $attributes ) {
 		return $attributes;
 	}
 
-	/**
-	 * This is our workaround to enforce max sizing with layout=responsive.
-	 *
-	 * We want elements to not grow beyond their width and shrink to fill the screen on viewports smaller than their width.
-	 *
-	 * See https://github.com/ampproject/amphtml/issues/1280#issuecomment-171533526
-	 * See https://github.com/Automattic/amp-wp/issues/101
-	 *
-	 * @param string[] $attributes {
-	 *      Attributes.
-	 *
-	 *      @type int $height
-	 *      @type int $width
-	 *      @type string $sizes
-	 *      @type string $class
-	 *      @type string $layout
-	 * }
-	 * @return string[]
-	 */
-	public function enforce_sizes_attribute( $attributes ) {
-		if ( ! isset( $attributes['width'], $attributes['height'] ) ) {
-			return $attributes;
-		}
-
-		$max_width = $attributes['width'];
-		if ( isset( $this->args['content_max_width'] ) && $max_width >= $this->args['content_max_width'] ) {
-			$max_width = $this->args['content_max_width'];
-		}
-
-		// Allows floats and integers but prevents negative values.
-		// Uses string format to prevent additional modification.
-		$attributes['sizes'] = sprintf(
-			'(min-width: %1$spx) %1$spx, 100vw',
-			max( 0, floatval( $max_width ) )
-		);
-
-		$this->add_or_append_attribute( $attributes, 'class', 'amp-wp-enforced-sizes' );
-
-		return $attributes;
-	}
-
 	/**
 	 * Adds or appends key and value to list of attributes
 	 *
diff --git a/includes/sanitizers/class-amp-iframe-sanitizer.php b/includes/sanitizers/class-amp-iframe-sanitizer.php
index 9dac35a8a3e..07c07875f72 100644
--- a/includes/sanitizers/class-amp-iframe-sanitizer.php
+++ b/includes/sanitizers/class-amp-iframe-sanitizer.php
@@ -79,9 +79,11 @@ public function sanitize() {
 			}
 
 			$this->did_convert_elements = true;
-
-			$new_attributes = $this->enforce_fixed_height( $new_attributes );
-			$new_attributes = $this->enforce_sizes_attribute( $new_attributes );
+			$new_attributes             = $this->set_layout( $new_attributes );
+			if ( empty( $new_attributes['layout'] ) && ! empty( $new_attributes['width'] ) && ! empty( $new_attributes['height'] ) ) {
+				$new_attributes['layout'] = 'intrinsic';
+				$this->add_or_append_attribute( $new_attributes, 'class', 'amp-wp-enforced-sizes' );
+			}
 
 			$new_node = AMP_DOM_Utils::create_node( $this->dom, 'amp-iframe', $new_attributes );
 
@@ -126,8 +128,7 @@ public function sanitize() {
 	 * @return array Returns HTML attributes; removes any not specifically declared above from input.
 	 */
 	private function filter_attributes( $attributes ) {
-		$out          = array();
-		$out['style'] = 'max-width:100%'; // AMP_Style_Sanitizer will move this to the amp-custom style.
+		$out = array();
 
 		foreach ( $attributes as $name => $value ) {
 			switch ( $name ) {
diff --git a/includes/sanitizers/class-amp-img-sanitizer.php b/includes/sanitizers/class-amp-img-sanitizer.php
index 5a9bd2f5d7c..41c9cab503b 100644
--- a/includes/sanitizers/class-amp-img-sanitizer.php
+++ b/includes/sanitizers/class-amp-img-sanitizer.php
@@ -73,7 +73,7 @@ public function sanitize() {
 				continue;
 			}
 
-			if ( ! $node->hasAttribute( 'src' ) || '' === $node->getAttribute( 'src' ) ) {
+			if ( ! $node->hasAttribute( 'src' ) || '' === trim( $node->getAttribute( 'src' ) ) ) {
 				$this->remove_invalid_child( $node );
 				continue;
 			}
@@ -119,7 +119,6 @@ private function filter_attributes( $attributes ) {
 				case 'alt':
 				case 'class':
 				case 'srcset':
-				case 'sizes':
 				case 'on':
 				case 'attribution':
 					$out[ $name ] = $value;
@@ -130,6 +129,10 @@ private function filter_attributes( $attributes ) {
 					$out[ $name ] = $this->sanitize_dimension( $value, $name );
 					break;
 
+				case 'data-amp-layout':
+					$out['layout'] = $value;
+					break;
+
 				default:
 					break;
 			}
@@ -204,7 +207,10 @@ private function adjust_and_replace_nodes_in_array_map( $node_lists ) {
 	private function adjust_and_replace_node( $node ) {
 		$old_attributes = AMP_DOM_Utils::get_node_attributes_as_assoc_array( $node );
 		$new_attributes = $this->filter_attributes( $old_attributes );
-		$new_attributes = $this->enforce_sizes_attribute( $new_attributes );
+		$this->add_or_append_attribute( $new_attributes, 'class', 'amp-wp-enforced-sizes' );
+		if ( empty( $new_attributes['layout'] ) && ! empty( $new_attributes['height'] ) && ! empty( $new_attributes['width'] ) ) {
+			$new_attributes['layout'] = 'intrinsic';
+		}
 		if ( $this->is_gif_url( $new_attributes['src'] ) ) {
 			$this->did_convert_elements = true;
 
diff --git a/includes/sanitizers/class-amp-video-sanitizer.php b/includes/sanitizers/class-amp-video-sanitizer.php
index 1dadfcc00eb..0512da17754 100644
--- a/includes/sanitizers/class-amp-video-sanitizer.php
+++ b/includes/sanitizers/class-amp-video-sanitizer.php
@@ -49,9 +49,10 @@ public function sanitize() {
 			$old_attributes = AMP_DOM_Utils::get_node_attributes_as_assoc_array( $node );
 
 			$new_attributes = $this->filter_attributes( $old_attributes );
-
-			$new_attributes = $this->enforce_fixed_height( $new_attributes );
-			$new_attributes = $this->enforce_sizes_attribute( $new_attributes );
+			$new_attributes = $this->set_layout( $new_attributes );
+			if ( empty( $new_attributes['layout'] ) && ! empty( $new_attributes['width'] ) && ! empty( $new_attributes['height'] ) ) {
+				$new_attributes['layout'] = 'responsive';
+			}
 
 			$new_node = AMP_DOM_Utils::create_node( $this->dom, 'amp-video', $new_attributes );
 
@@ -124,8 +125,7 @@ public function sanitize() {
 	 * @return array Returns HTML attributes; removes any not specifically declared above from input.
 	 */
 	private function filter_attributes( $attributes ) {
-		$out          = array();
-		$out['style'] = 'max-width:100%'; // Note that this will get moved to amp-custom style by AMP_Style_Sanitizer.
+		$out = array();
 
 		foreach ( $attributes as $name => $value ) {
 			switch ( $name ) {
diff --git a/includes/utils/class-amp-validation-utils.php b/includes/utils/class-amp-validation-utils.php
index bec91a67969..eff7c4cef3e 100644
--- a/includes/utils/class-amp-validation-utils.php
+++ b/includes/utils/class-amp-validation-utils.php
@@ -214,6 +214,7 @@ public static function init() {
 		add_filter( 'bulk_actions-edit-' . self::POST_TYPE_SLUG, array( __CLASS__, 'add_bulk_action' ), 10, 2 );
 		add_filter( 'handle_bulk_actions-edit-' . self::POST_TYPE_SLUG, array( __CLASS__, 'handle_bulk_action' ), 10, 3 );
 		add_action( 'admin_notices', array( __CLASS__, 'remaining_error_notice' ) );
+		add_action( 'admin_notices', array( __CLASS__, 'persistent_object_caching_notice' ) );
 		add_action( 'post_action_' . self::RECHECK_ACTION, array( __CLASS__, 'handle_inline_recheck' ) );
 		add_action( 'admin_menu', array( __CLASS__, 'remove_publish_meta_box' ) );
 		add_action( 'admin_menu', array( __CLASS__, 'add_admin_menu_validation_status_count' ) );
@@ -1791,4 +1792,21 @@ public static function get_recheck_link( $post, $redirect_url, $recheck_url = nu
 		);
 	}
 
+	/**
+	 * Outputs an admin notice if persistent object cache is not present.
+	 *
+	 * @return void
+	 */
+	public static function persistent_object_caching_notice() {
+		if ( ! wp_using_ext_object_cache() && 'toplevel_page_amp-options' === get_current_screen()->id ) {
+			printf(
+				'<div class="notice notice-warning"><p>%s <a href="%s">%s</a></p></div>',
+				esc_html__( 'The AMP plugin performs at its best when persistent object cache is enabled.', 'amp' ),
+				esc_url( 'https://codex.wordpress.org/Class_Reference/WP_Object_Cache#Persistent_Caching' ),
+				esc_html__( 'More details', 'amp' )
+			);
+		}
+	}
+
 }
+
diff --git a/phpunit.xml b/phpunit.xml
index a2b80c5bb36..4d7d8f842a4 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -22,6 +22,7 @@
 			<directory suffix=".php">./</directory>
 			<exclude>
 				<directory suffix=".php">dev-lib</directory>
+				<directory suffix=".php">svn</directory>
 				<directory suffix=".php">node_modules</directory>
 				<directory suffix=".php">tests</directory>
 				<directory suffix=".php">vendor</directory>
diff --git a/tests/test-amp-analytics-options.php b/tests/test-amp-analytics-options.php
index a1c0e872c58..c4caceca43a 100644
--- a/tests/test-amp-analytics-options.php
+++ b/tests/test-amp-analytics-options.php
@@ -216,7 +216,7 @@ public function test_two_analytics_components_added() {
 	/**
 	 * Test amp_get_analytics()
 	 *
-	 * @covers amp_get_analytics()
+	 * @covers \amp_get_analytics()
 	 */
 	public function test_amp_get_analytics() {
 		$this->insert_one_option(
@@ -243,7 +243,7 @@ public function test_amp_get_analytics() {
 	/**
 	 * Test amp_print_analytics()
 	 *
-	 * @covers amp_print_analytics()
+	 * @covers \amp_print_analytics()
 	 */
 	public function test_amp_print_analytics() {
 		$this->insert_one_option(
diff --git a/tests/test-amp-frontend-actions.php b/tests/test-amp-frontend-actions.php
new file mode 100644
index 00000000000..31809e82e65
--- /dev/null
+++ b/tests/test-amp-frontend-actions.php
@@ -0,0 +1,87 @@
+<?php
+/**
+ * Test AMP frontend actions.
+ *
+ * @package AMP
+ */
+
+/**
+ * Test functions in includes/amp-frontend-actions.php
+ */
+class Test_AMP_Frontend_Actions extends WP_UnitTestCase {
+
+	/**
+	 * Set up.
+	 */
+	public function setUp() {
+		parent::setUp();
+		require_once AMP__DIR__ . '/includes/amp-helper-functions.php';
+		amp_add_frontend_actions();
+	}
+
+	/**
+	 * After a test method runs, reset any state in WordPress the test method might have changed.
+	 */
+	public function tearDown() {
+		remove_theme_support( 'amp' );
+		parent::tearDown();
+	}
+
+	/**
+	 * Test that hook is added.
+	 *
+	 * @covers \amp_add_frontend_actions()
+	 */
+	public function test_has_hook() {
+		$this->assertEquals( 10, has_action( 'wp_head', 'amp_frontend_add_canonical' ) );
+	}
+
+	/**
+	 * URLs to test amphtml link.
+	 *
+	 * @return array
+	 */
+	public function get_amphtml_urls() {
+		$post_id = $this->factory()->post->create();
+		return array(
+			'home' => array(
+				home_url( '/' ),
+				add_query_arg( amp_get_slug(), '', home_url( '/' ) ),
+			),
+			'404'  => array(
+				home_url( '/no-existe/' ),
+				add_query_arg( amp_get_slug(), '', home_url( '/no-existe/' ) ),
+			),
+			'post' => array(
+				get_permalink( $post_id ),
+				amp_get_permalink( $post_id ),
+			),
+		);
+	}
+
+	/**
+	 * Adding link when theme support is not present.
+	 *
+	 * @dataProvider get_amphtml_urls
+	 * @covers \amp_frontend_add_canonical()
+	 * @param string $canonical_url Canonical URL.
+	 * @param string $amphtml_url   The amphtml URL.
+	 */
+	public function test_amp_frontend_add_canonical( $canonical_url, $amphtml_url ) {
+		$this->go_to( $canonical_url );
+		ob_start();
+		amp_frontend_add_canonical();
+		$output = ob_get_clean();
+		$this->assertEquals(
+			sprintf( '<link rel="amphtml" href="%s">', esc_url( $amphtml_url ) ),
+			$output
+		);
+
+		// Make sure adding the filter hides the amphtml link.
+		add_filter( 'amp_frontend_show_canonical', '__return_false' );
+		ob_start();
+		amp_frontend_add_canonical();
+		$output = ob_get_clean();
+		$this->assertEmpty( $output );
+	}
+}
diff --git a/tests/test-amp-helper-functions.php b/tests/test-amp-helper-functions.php
index 3dd206da7aa..b29f3eefaa7 100644
--- a/tests/test-amp-helper-functions.php
+++ b/tests/test-amp-helper-functions.php
@@ -35,7 +35,7 @@ public function return_example_url( $url, $post_id ) {
 	/**
 	 * Test amp_get_slug().
 	 *
-	 * @covers amp_get_slug()
+	 * @covers \amp_get_slug()
 	 */
 	public function test_amp_get_slug() {
 		$this->assertSame( 'amp', amp_get_slug() );
@@ -181,8 +181,8 @@ public function capture_filter_call( $value ) {
 	/**
 	 * Test script registering.
 	 *
-	 * @covers amp_register_default_scripts()
-	 * @covers amp_filter_script_loader_tag()
+	 * @covers \amp_register_default_scripts()
+	 * @covers \amp_filter_script_loader_tag()
 	 * @global WP_Scripts $wp_scripts
 	 */
 	public function test_script_registering() {
@@ -223,7 +223,7 @@ public function test_script_registering() {
 	/**
 	 * Test amp_get_content_embed_handlers().
 	 *
-	 * @covers amp_get_content_embed_handlers()
+	 * @covers \amp_get_content_embed_handlers()
 	 */
 	public function test_amp_get_content_embed_handlers() {
 		$post = $this->factory()->post->create_and_get();
@@ -249,7 +249,7 @@ public function test_amp_get_content_embed_handlers() {
 	/**
 	 * Test deprecated $post param for amp_get_content_embed_handlers().
 	 *
-	 * @covers amp_get_content_embed_handlers()
+	 * @covers \amp_get_content_embed_handlers()
 	 */
 	public function test_amp_get_content_embed_handlers_deprecated_param() {
 		$post = $this->factory()->post->create_and_get();
@@ -261,7 +261,7 @@ public function test_amp_get_content_embed_handlers_deprecated_param() {
 	/**
 	 * Test amp_get_content_sanitizers().
 	 *
-	 * @covers amp_get_content_sanitizers()
+	 * @covers \amp_get_content_sanitizers()
 	 */
 	public function test_amp_get_content_sanitizers() {
 		$post = $this->factory()->post->create_and_get();
@@ -299,7 +299,7 @@ public function test_amp_get_content_sanitizers() {
 	/**
 	 * Test deprecated $post param for amp_get_content_sanitizers().
 	 *
-	 * @covers amp_get_content_sanitizers()
+	 * @covers \amp_get_content_sanitizers()
 	 */
 	public function test_amp_get_content_sanitizers_deprecated_param() {
 		$post = $this->factory()->post->create_and_get();
diff --git a/tests/test-amp-iframe-sanitizer.php b/tests/test-amp-iframe-sanitizer.php
index d451f4715be..be2f00becfd 100644
--- a/tests/test-amp-iframe-sanitizer.php
+++ b/tests/test-amp-iframe-sanitizer.php
@@ -10,57 +10,57 @@ public function get_data() {
 
 			'simple_iframe' => array(
 				'<iframe src="https://example.com/embed/132886713" width="500" height="281" frameborder="0" class="iframe-class" allowtransparency="false" allowfullscreen></iframe>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/embed/132886713" width="500" height="281" frameborder="0" class="iframe-class amp-wp-enforced-sizes" allowfullscreen="" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw"></amp-iframe>',
+				'<amp-iframe src="https://example.com/embed/132886713" width="500" height="281" frameborder="0" class="iframe-class amp-wp-enforced-sizes" allowfullscreen="" sandbox="allow-scripts allow-same-origin" layout="intrinsic"></amp-iframe>',
 			),
 
 			'force_https' => array(
 				'<iframe src="http://example.com/embed/132886713" width="500" height="281" frameborder="0" class="iframe-class" allowtransparency="false" allowfullscreen></iframe>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/embed/132886713" width="500" height="281" frameborder="0" class="iframe-class amp-wp-enforced-sizes" allowfullscreen="" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw"></amp-iframe>',
+				'<amp-iframe src="https://example.com/embed/132886713" width="500" height="281" frameborder="0" class="iframe-class amp-wp-enforced-sizes" allowfullscreen="" sandbox="allow-scripts allow-same-origin" layout="intrinsic"></amp-iframe>',
 			),
 
 			'iframe_without_dimensions' => array(
 				'<iframe src="https://example.com/video/132886713"></iframe>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/video/132886713" sandbox="allow-scripts allow-same-origin" height="400" layout="fixed-height"></amp-iframe>',
+				'<amp-iframe src="https://example.com/video/132886713" sandbox="allow-scripts allow-same-origin" height="400" layout="fixed-height"></amp-iframe>',
 			),
 
 			'iframe_with_height_only' => array(
 				'<iframe src="https://example.com/video/132886713" height="400"></iframe>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/video/132886713" height="400" sandbox="allow-scripts allow-same-origin" layout="fixed-height"></amp-iframe>',
+				'<amp-iframe src="https://example.com/video/132886713" height="400" sandbox="allow-scripts allow-same-origin" layout="fixed-height"></amp-iframe>',
 			),
 
 			'iframe_with_width_only' => array(
 				'<iframe src="https://example.com/video/132886713" width="600"></iframe>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/video/132886713" sandbox="allow-scripts allow-same-origin" height="400" layout="fixed-height"></amp-iframe>',
+				'<amp-iframe src="https://example.com/video/132886713" sandbox="allow-scripts allow-same-origin" height="400" layout="fixed-height"></amp-iframe>',
 			),
 
 			'iframe_with_invalid_frameborder' => array(
 				'<iframe src="https://example.com/embed/132886713" width="500" height="281" frameborder="no"></iframe>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/embed/132886713" width="500" height="281" frameborder="0" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe>',
+				'<amp-iframe src="https://example.com/embed/132886713" width="500" height="281" frameborder="0" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe>',
 			),
 
 			'iframe_with_1_frameborder' => array(
 				'<iframe src="https://example.com/embed/132886713" width="500" height="281" frameborder=1></iframe>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/embed/132886713" width="500" height="281" frameborder="1" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe>',
+				'<amp-iframe src="https://example.com/embed/132886713" width="500" height="281" frameborder="1" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe>',
 			),
 
 			'simple_iframe_with_sandbox' => array(
 				'<iframe src="https://example.com/embed/132886713" width="500" height="281" sandbox="allow-same-origin"></iframe>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/embed/132886713" width="500" height="281" sandbox="allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe>',
+				'<amp-iframe src="https://example.com/embed/132886713" width="500" height="281" sandbox="allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe>',
 			),
 
 			'iframe_with_blacklisted_attribute' => array(
 				'<iframe src="https://example.com/embed/132886713" width="500" height="281" scrolling="auto"></iframe>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/embed/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe>',
+				'<amp-iframe src="https://example.com/embed/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe>',
 			),
 
 			'iframe_with_sizes_attribute_is_overridden' => array(
-				'<iframe src="https://example.com/iframe" width="500" height="281" sizes="(min-width: 100px) 300px, 90vw"></iframe>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/iframe" width="500" height="281" sizes="(min-width: 500px) 500px, 100vw" sandbox="allow-scripts allow-same-origin" class="amp-wp-enforced-sizes"></amp-iframe>',
+				'<iframe src="https://example.com/iframe" width="500" height="281"></iframe>',
+				'<amp-iframe src="https://example.com/iframe" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe>',
 			),
 
 			'iframe_with_protocol_relative_url' => array(
 				'<iframe src="//example.com/video/132886713"></iframe>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/video/132886713" sandbox="allow-scripts allow-same-origin" height="400" layout="fixed-height"></amp-iframe>',
+				'<amp-iframe src="https://example.com/video/132886713" sandbox="allow-scripts allow-same-origin" height="400" layout="fixed-height"></amp-iframe>',
 			),
 
 			'multiple_same_iframe' => array(
@@ -69,7 +69,7 @@ public function get_data() {
 <iframe src="https://example.com/embed/132886713" width="500" height="281"></iframe>
 <iframe src="https://example.com/embed/132886713" width="500" height="281"></iframe>
 				',
-				'<amp-iframe style="max-width:100%" src="https://example.com/embed/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe style="max-width:100%" src="https://example.com/embed/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe style="max-width:100%" src="https://example.com/embed/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe>',
+				'<amp-iframe src="https://example.com/embed/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe src="https://example.com/embed/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe src="https://example.com/embed/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe>',
 			),
 
 			'multiple_different_iframes' => array(
@@ -78,19 +78,19 @@ public function get_data() {
 <iframe src="https://example.com/embed/67890" width="280" height="501"></iframe>
 <iframe src="https://example.com/embed/11111" width="700" height="601"></iframe>
 				',
-				'<amp-iframe style="max-width:100%" src="https://example.com/embed/12345" width="500" height="281" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe style="max-width:100%" src="https://example.com/embed/67890" width="280" height="501" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 280px) 280px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe style="max-width:100%" src="https://example.com/embed/11111" width="700" height="601" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 700px) 700px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe>',
+				'<amp-iframe src="https://example.com/embed/12345" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe src="https://example.com/embed/67890" width="280" height="501" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe src="https://example.com/embed/11111" width="700" height="601" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe>',
 			),
 			'iframe_in_p_tag' => array(
 				'<p><iframe src="https://example.com/video/132886713" width="500" height="281"></iframe></p>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/video/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe>',
+				'<amp-iframe src="https://example.com/video/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe>',
 			),
 			'multiple_iframes_in_p_tag' => array(
 				'<p><iframe src="https://example.com/video/132886713" width="500" height="281"></iframe><iframe src="https://example.com/video/132886714" width="500" height="281"></iframe></p>',
-				'<amp-iframe style="max-width:100%" src="https://example.com/video/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe style="max-width:100%" src="https://example.com/video/132886714" width="500" height="281" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe>',
+				'<amp-iframe src="https://example.com/video/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe src="https://example.com/video/132886714" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe>',
 			),
 			'multiple_iframes_and_contents_in_p_tag' => array(
 				'<p>contents<iframe src="https://example.com/video/132886713" width="500" height="281"></iframe><iframe src="https://example.com/video/132886714" width="500" height="281"></iframe></p>',
-				'<p>contents</p><amp-iframe style="max-width:100%" src="https://example.com/video/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe style="max-width:100%" src="https://example.com/video/132886714" width="500" height="281" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"></amp-iframe>',
+				'<p>contents</p><amp-iframe src="https://example.com/video/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe><amp-iframe src="https://example.com/video/132886714" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"></amp-iframe>',
 			),
 		);
 	}
@@ -160,7 +160,7 @@ public function test_get_scripts__did_convert() {
 
 	public function test__args__placeholder() {
 		$source = '<iframe src="https://example.com/video/132886713" width="500" height="281"></iframe>';
-		$expected = '<amp-iframe style="max-width:100%" src="https://example.com/video/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" sizes="(min-width: 500px) 500px, 100vw" class="amp-wp-enforced-sizes"><div placeholder="" class="amp-wp-iframe-placeholder"></div></amp-iframe>';
+		$expected = '<amp-iframe src="https://example.com/video/132886713" width="500" height="281" sandbox="allow-scripts allow-same-origin" layout="intrinsic" class="amp-wp-enforced-sizes"><div placeholder="" class="amp-wp-iframe-placeholder"></div></amp-iframe>';
 
 		$dom = AMP_DOM_Utils::get_dom_from_content( $source );
 		$sanitizer = new AMP_Iframe_Sanitizer( $dom, array(
diff --git a/tests/test-amp-img-sanitizer.php b/tests/test-amp-img-sanitizer.php
index a6a400264a1..0f15018618c 100644
--- a/tests/test-amp-img-sanitizer.php
+++ b/tests/test-amp-img-sanitizer.php
@@ -27,79 +27,89 @@ public function get_data() {
 				'<p></p>',
 			),
 
+			'image_with_layout'                        => array(
+				'<img src="http://placehold.it/100x100" data-amp-layout="fill" width="100" height="100" />',
+				'<amp-img src="http://placehold.it/100x100" layout="fill" width="100" height="100" class="amp-wp-enforced-sizes"></amp-img>',
+			),
+
+			'image_with_spaces_only_src'               => array(
+				'<p><img src="    " width="300" height="300" /></p>',
+				'<p></p>',
+			),
+
 			'image_with_empty_width_and_height'        => array(
 				'<p><img src="http://placehold.it/300x300" width="" height="" /></p>',
-				'<p><amp-img src="http://placehold.it/300x300" width="600" height="400" class="amp-wp-unknown-size amp-wp-enforced-sizes" sizes="(min-width: 600px) 600px, 100vw"></amp-img></p>',
+				'<p><amp-img src="http://placehold.it/300x300" width="600" height="400" class="amp-wp-unknown-size amp-wp-enforced-sizes" layout="intrinsic"></amp-img></p>',
 			),
 
 			'image_with_empty_width'                   => array(
 				'<p><img src="http://placehold.it/300x300" width="" height="300" /></p>',
-				'<p><amp-img src="http://placehold.it/300x300" width="600" height="300" class="amp-wp-unknown-size amp-wp-unknown-width amp-wp-enforced-sizes" sizes="(min-width: 600px) 600px, 100vw"></amp-img></p>',
+				'<p><amp-img src="http://placehold.it/300x300" width="600" height="300" class="amp-wp-unknown-size amp-wp-unknown-width amp-wp-enforced-sizes" layout="intrinsic"></amp-img></p>',
 			),
 
 			'image_with_empty_height'                  => array(
 				'<p><img src="http://placehold.it/300x300" width="300" height="" /></p>',
-				'<p><amp-img src="http://placehold.it/300x300" width="300" height="400" class="amp-wp-unknown-size amp-wp-unknown-height amp-wp-enforced-sizes" sizes="(min-width: 300px) 300px, 100vw"></amp-img></p>',
+				'<p><amp-img src="http://placehold.it/300x300" width="300" height="400" class="amp-wp-unknown-size amp-wp-unknown-height amp-wp-enforced-sizes" layout="intrinsic"></amp-img></p>',
 			),
 
 			'image_with_zero_width'                    => array(
 				'<p><img src="http://placehold.it/300x300" width="0" height="300" /></p>',
-				'<p><amp-img src="http://placehold.it/300x300" width="0" height="300" sizes="(min-width: 0px) 0px, 100vw" class="amp-wp-enforced-sizes"></amp-img></p>',
+				'<p><amp-img src="http://placehold.it/300x300" width="0" height="300" class="amp-wp-enforced-sizes"></amp-img></p>',
 			),
 
 			'image_with_zero_width_and_height'         => array(
 				'<p><img src="http://placehold.it/300x300" width="0" height="0" /></p>',
-				'<p><amp-img src="http://placehold.it/300x300" width="0" height="0" sizes="(min-width: 0px) 0px, 100vw" class="amp-wp-enforced-sizes"></amp-img></p>',
+				'<p><amp-img src="http://placehold.it/300x300" width="0" height="0" class="amp-wp-enforced-sizes"></amp-img></p>',
 			),
 
 			'image_with_decimal_width'                 => array(
 				'<p><img src="http://placehold.it/300x300" width="299.5" height="300" /></p>',
-				'<p><amp-img src="http://placehold.it/300x300" width="299.5" height="300" sizes="(min-width: 299.5px) 299.5px, 100vw" class="amp-wp-enforced-sizes"></amp-img></p>',
+				'<p><amp-img src="http://placehold.it/300x300" width="299.5" height="300" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img></p>',
 			),
 
 			'image_with_self_closing_tag'              => array(
 				'<img src="http://placehold.it/350x150" width="350" height="150" alt="Placeholder!" />',
-				'<amp-img src="http://placehold.it/350x150" width="350" height="150" alt="Placeholder!" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-img>',
+				'<amp-img src="http://placehold.it/350x150" width="350" height="150" alt="Placeholder!" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img>',
 			),
 
 			'image_with_no_end_tag'                    => array(
 				'<img src="http://placehold.it/350x150" width="350" height="150" alt="Placeholder!">',
-				'<amp-img src="http://placehold.it/350x150" width="350" height="150" alt="Placeholder!" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-img>',
+				'<amp-img src="http://placehold.it/350x150" width="350" height="150" alt="Placeholder!" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img>',
 			),
 
 			'image_with_end_tag'                       => array(
 				'<img src="http://placehold.it/350x150" width="350" height="150" alt="Placeholder!"></img>',
-				'<amp-img src="http://placehold.it/350x150" width="350" height="150" alt="Placeholder!" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-img>',
+				'<amp-img src="http://placehold.it/350x150" width="350" height="150" alt="Placeholder!" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img>',
 			),
 
 			'image_with_on_attribute'                  => array(
 				'<img src="http://placehold.it/350x150" on="tap:my-lightbox" width="350" height="150" />',
-				'<amp-img src="http://placehold.it/350x150" on="tap:my-lightbox" width="350" height="150" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-img>',
+				'<amp-img src="http://placehold.it/350x150" on="tap:my-lightbox" width="350" height="150" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img>',
 			),
 
 			'image_with_blacklisted_attribute'         => array(
 				'<img src="http://placehold.it/350x150" width="350" height="150" style="border: 1px solid red;" />',
-				'<amp-img src="http://placehold.it/350x150" width="350" height="150" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-img>',
+				'<amp-img src="http://placehold.it/350x150" width="350" height="150" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img>',
 			),
 
 			'image_with_no_dimensions_is_forced_dimensions' => array(
 				'<img src="http://placehold.it/350x150" />',
-				'<amp-img src="http://placehold.it/350x150" width="600" height="400" class="amp-wp-unknown-size amp-wp-enforced-sizes" sizes="(min-width: 600px) 600px, 100vw"></amp-img>',
+				'<amp-img src="http://placehold.it/350x150" width="600" height="400" class="amp-wp-unknown-size amp-wp-enforced-sizes" layout="intrinsic"></amp-img>',
 			),
 
 			'image_with_sizes_attribute_is_overridden' => array(
-				'<img src="http://placehold.it/350x150" width="350" height="150" sizes="(min-width: 100px) 300px, 90vw" />',
-				'<amp-img src="http://placehold.it/350x150" width="350" height="150" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-img>',
+				'<img src="http://placehold.it/350x150" width="350" height="150"  />',
+				'<amp-img src="http://placehold.it/350x150" width="350" height="150" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img>',
 			),
 
 			'gif_image_conversion'                     => array(
 				'<img src="http://placehold.it/350x150.gif" width="350" height="150" alt="Placeholder!" />',
-				'<amp-anim src="http://placehold.it/350x150.gif" width="350" height="150" alt="Placeholder!" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-anim>',
+				'<amp-anim src="http://placehold.it/350x150.gif" width="350" height="150" alt="Placeholder!" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-anim>',
 			),
 
 			'gif_image_url_with_querystring'           => array(
 				'<img src="http://placehold.it/350x150.gif?foo=bar" width="350" height="150" alt="Placeholder!" />',
-				'<amp-anim src="http://placehold.it/350x150.gif?foo=bar" width="350" height="150" alt="Placeholder!" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-anim>',
+				'<amp-anim src="http://placehold.it/350x150.gif?foo=bar" width="350" height="150" alt="Placeholder!" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-anim>',
 			),
 
 			'multiple_same_image'                      => array(
@@ -108,7 +118,7 @@ public function get_data() {
 <img src="http://placehold.it/350x150" width="350" height="150" />
 <img src="http://placehold.it/350x150" width="350" height="150" />
 				',
-				'<amp-img src="http://placehold.it/350x150" width="350" height="150" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-img><amp-img src="http://placehold.it/350x150" width="350" height="150" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-img><amp-img src="http://placehold.it/350x150" width="350" height="150" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-img><amp-img src="http://placehold.it/350x150" width="350" height="150" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-img>',
+				'<amp-img src="http://placehold.it/350x150" width="350" height="150" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img><amp-img src="http://placehold.it/350x150" width="350" height="150" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img><amp-img src="http://placehold.it/350x150" width="350" height="150" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img><amp-img src="http://placehold.it/350x150" width="350" height="150" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img>',
 			),
 
 			'multiple_different_images'                => array(
@@ -116,7 +126,7 @@ public function get_data() {
 <img src="http://placehold.it/360x160" width="360" height="160" />
 <img src="http://placehold.it/370x170" width="370" height="170" />
 <img src="http://placehold.it/380x180" width="380" height="180" />',
-				'<amp-img src="http://placehold.it/350x150" width="350" height="150" sizes="(min-width: 350px) 350px, 100vw" class="amp-wp-enforced-sizes"></amp-img><amp-img src="http://placehold.it/360x160" width="360" height="160" sizes="(min-width: 360px) 360px, 100vw" class="amp-wp-enforced-sizes"></amp-img><amp-img src="http://placehold.it/370x170" width="370" height="170" sizes="(min-width: 370px) 370px, 100vw" class="amp-wp-enforced-sizes"></amp-img><amp-img src="http://placehold.it/380x180" width="380" height="180" sizes="(min-width: 380px) 380px, 100vw" class="amp-wp-enforced-sizes"></amp-img>',
+				'<amp-img src="http://placehold.it/350x150" width="350" height="150" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img><amp-img src="http://placehold.it/360x160" width="360" height="160" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img><amp-img src="http://placehold.it/370x170" width="370" height="170" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img><amp-img src="http://placehold.it/380x180" width="380" height="180" class="amp-wp-enforced-sizes" layout="intrinsic"></amp-img>',
 			),
 		);
 	}
diff --git a/tests/test-amp-video-sanitizer.php b/tests/test-amp-video-sanitizer.php
index e5cb4308651..5a0f989db05 100644
--- a/tests/test-amp-video-sanitizer.php
+++ b/tests/test-amp-video-sanitizer.php
@@ -10,42 +10,42 @@ public function get_data() {
 
 			'simple_video' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4"></video>',
-				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video width="300" height="300" src="https://example.com/video.mp4" layout="responsive"></amp-video>',
 			),
 
 			'video_without_dimensions' => array(
 				'<video src="https://example.com/file.mp4"></video>',
-				'<amp-video style="max-width:100%" src="https://example.com/file.mp4" height="400" layout="fixed-height"></amp-video>',
+				'<amp-video src="https://example.com/file.mp4" height="400" layout="fixed-height"></amp-video>',
 			),
 
 			'autoplay_attribute' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4" autoplay></video>',
-				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" autoplay="" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video width="300" height="300" src="https://example.com/video.mp4" autoplay="" layout="responsive"></amp-video>',
 			),
 
 			'autoplay_attribute__false' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4" autoplay="false"></video>',
-				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video width="300" height="300" src="https://example.com/video.mp4" layout="responsive"></amp-video>',
 			),
 
 			'video_with_whitelisted_attributes__enabled' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4" controls loop="true" muted="muted"></video>',
-				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" controls="" loop="" muted="" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video width="300" height="300" src="https://example.com/video.mp4" controls="" loop="" muted="" layout="responsive"></amp-video>',
 			),
 
 			'video_with_whitelisted_attributes__disabled' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4" controls="false" loop="false" muted="false"></video>',
-				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video width="300" height="300" src="https://example.com/video.mp4" layout="responsive"></amp-video>',
 			),
 
 			'video_with_blacklisted_attribute' => array(
 				'<video width="300" height="300" src="https://example.com/video.mp4" style="border-color: red;"></video>',
-				'<amp-video style="max-width:100%" width="300" height="300" src="https://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video width="300" height="300" src="https://example.com/video.mp4" layout="responsive"></amp-video>',
 			),
 
 			'video_with_sizes_attribute_is_overridden' => array(
-				'<video width="300" height="200" src="https://example.com/file.mp4" sizes="(min-width: 100px) 200px, 90vw"></video>',
-				'<amp-video style="max-width:100%" width="300" height="200" src="https://example.com/file.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<video width="300" height="200" src="https://example.com/file.mp4"></video>',
+				'<amp-video width="300" height="200" src="https://example.com/file.mp4" layout="responsive"></amp-video>',
 			),
 
 			'video_with_children' => array(
@@ -53,7 +53,7 @@ public function get_data() {
 	<source src="https://example.com/video.mp4" type="video/mp4">
 	<source src="https://example.com/video.ogv" type="video/ogg">
 </video>',
-				'<amp-video style="max-width:100%" width="480" height="300" poster="https://example.com/video-image.gif" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"><source src="https://example.com/video.mp4" type="video/mp4"><source src="https://example.com/video.ogv" type="video/ogg"></amp-video>',
+				'<amp-video width="480" height="300" poster="https://example.com/video-image.gif" layout="responsive"><source src="https://example.com/video.mp4" type="video/mp4"><source src="https://example.com/video.ogv" type="video/ogg"></amp-video>',
 			),
 
 			'multiple_same_video' => array(
@@ -61,19 +61,19 @@ public function get_data() {
 <video src="https://example.com/video.mp4" width="480" height="300"></video>
 <video src="https://example.com/video.mp4" width="480" height="300"></video>
 <video src="https://example.com/video.mp4" width="480" height="300"></video>',
-				'<amp-video style="max-width:100%" src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video style="max-width:100%" src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video style="max-width:100%" src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video style="max-width:100%" src="https://example.com/video.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video src="https://example.com/video.mp4" width="480" height="300" layout="responsive"></amp-video><amp-video src="https://example.com/video.mp4" width="480" height="300" layout="responsive"></amp-video><amp-video src="https://example.com/video.mp4" width="480" height="300" layout="responsive"></amp-video><amp-video src="https://example.com/video.mp4" width="480" height="300" layout="responsive"></amp-video>',
 			),
 
 			'multiple_different_videos' => array(
 				'<video src="https://example.com/video1.mp4" width="480" height="300"></video>
 <video src="https://example.com/video2.ogv" width="300" height="480"></video>
 <video src="https://example.com/video3.webm" height="100" width="200"></video>',
-				'<amp-video style="max-width:100%" src="https://example.com/video1.mp4" width="480" height="300" sizes="(min-width: 480px) 480px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video style="max-width:100%" src="https://example.com/video2.ogv" width="300" height="480" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video><amp-video style="max-width:100%" src="https://example.com/video3.webm" height="100" width="200" sizes="(min-width: 200px) 200px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video src="https://example.com/video1.mp4" width="480" height="300" layout="responsive"></amp-video><amp-video src="https://example.com/video2.ogv" width="300" height="480" layout="responsive"></amp-video><amp-video src="https://example.com/video3.webm" height="100" width="200" layout="responsive"></amp-video>',
 			),
 
 			'https_not_required' => array(
 				'<video width="300" height="300" src="http://example.com/video.mp4"></video>',
-				'<amp-video style="max-width:100%" width="300" height="300" src="http://example.com/video.mp4" sizes="(min-width: 300px) 300px, 100vw" class="amp-wp-enforced-sizes"></amp-video>',
+				'<amp-video width="300" height="300" src="http://example.com/video.mp4" layout="responsive"></amp-video>',
 			),
 		);
 	}
diff --git a/tests/test-amp.php b/tests/test-amp.php
index 19b68d9ad26..d78bc2edaab 100644
--- a/tests/test-amp.php
+++ b/tests/test-amp.php
@@ -21,7 +21,7 @@ public function tearDown() {
 	/**
 	 * Test amp_is_canonical().
 	 *
-	 * @covers amp_is_canonical()
+	 * @covers \amp_is_canonical()
 	 */
 	public function test_amp_is_canonical() {
 		remove_theme_support( 'amp' );
diff --git a/tests/test-class-amp-base-sanitizer.php b/tests/test-class-amp-base-sanitizer.php
index f3cf1db37c7..8902bb297cf 100644
--- a/tests/test-class-amp-base-sanitizer.php
+++ b/tests/test-class-amp-base-sanitizer.php
@@ -13,136 +13,22 @@
 class AMP_Base_Sanitizer_Test extends WP_UnitTestCase {
 
 	/**
-	 * Get enforce sizes data.
+	 * Gets data for test_set_layout().
 	 *
-	 * @return array Data
+	 * @return array
 	 */
-	public function get_enforce_sizes_data() {
-		return array(
-			'already_has_sizes'                            => array(
-				array(
-					'sizes' => 'blah',
-				),
-				array(
-					'sizes' => 'blah',
-				),
-			),
-
-			'empty'                                        => array(
-				array(),
-				array(),
-			),
-
-			'no_width'                                     => array(
-				array(
-					'height' => 100,
-				),
-				array(
-					'height' => 100,
-				),
-			),
-
-			'no_height'                                    => array(
-				array(
-					'width' => 200,
-				),
-				array(
-					'width' => 200,
-				),
-			),
-
-			'enforce_sizes_no_class'                       => array(
-				array(
-					'width'  => 200,
-					'height' => 100,
-				),
-				array(
-					'width'  => 200,
-					'height' => 100,
-					'sizes'  => '(min-width: 200px) 200px, 100vw',
-					'class'  => 'amp-wp-enforced-sizes',
-				),
-			),
-
-			'enforce_sizes_has_class'                      => array(
-				array(
-					'width'  => 200,
-					'height' => 100,
-					'class'  => 'my-class',
-				),
-				array(
-					'width'  => 200,
-					'height' => 100,
-					'sizes'  => '(min-width: 200px) 200px, 100vw',
-					'class'  => 'my-class amp-wp-enforced-sizes',
-				),
-			),
-
-			'enforce_sizes_with_bigger_content_max_width'  => array(
-				array(
-					'width'  => 250,
-					'height' => 100,
-				),
-				array(
-					'width'  => 250,
-					'height' => 100,
-					'sizes'  => '(min-width: 250px) 250px, 100vw',
-					'class'  => 'amp-wp-enforced-sizes',
-				),
-				array(
-					'content_max_width' => 500,
-				),
-			),
-
-			'enforce_sizes_with_smaller_content_max_width' => array(
-				array(
-					'width'  => 800,
-					'height' => 350,
-				),
-				array(
-					'width'  => 800,
-					'height' => 350,
-					'sizes'  => '(min-width: 675px) 675px, 100vw',
-					'class'  => 'amp-wp-enforced-sizes',
-				),
-				array(
-					'content_max_width' => 675,
-				),
-			),
-		);
-	}
-
-	/**
-	 * Test AMP_Base_Sanitizer::enforce_sizes_attribute().
-	 *
-	 * @dataProvider get_enforce_sizes_data
-	 * @param array $source_attributes   Source Attrs.
-	 * @param array $expected_attributes Expected Attrs.
-	 * @param array $args                Args.
-	 * @covers AMP_Base_Sanitizer::enforce_sizes_attribute()
-	 */
-	public function test_enforce_sizes_attribute( $source_attributes, $expected_attributes, $args = array() ) {
-		$sanitizer           = new AMP_Test_Stub_Sanitizer( new DOMDocument(), $args );
-		$returned_attributes = $sanitizer->enforce_sizes_attribute( $source_attributes );
-
-		$this->assertEquals( $expected_attributes, $returned_attributes );
-	}
-
-	/**
-	 * Get enforce fixed data.
-	 *
-	 * @return array Data.
-	 */
-	public function get_enforce_fixed_data() {
+	public function get_data() {
 		return array(
 			'both_dimensions_included' => array(
 				array(
 					'width'  => 100,
 					'height' => 100,
+					'layout' => 'responsive',
 				),
 				array(
 					'width'  => 100,
 					'height' => 100,
+					'layout' => 'responsive',
 				),
 			),
 
@@ -184,22 +70,32 @@ public function get_enforce_fixed_data() {
 					'layout' => 'fixed-height',
 				),
 			),
+
+			'no_layout_specified'      => array(
+				array(
+					'width'  => 100,
+					'height' => 100,
+				),
+				array(
+					'width'  => 100,
+					'height' => 100,
+				),
+			),
 		);
 	}
 
 	/**
-	 * Test AMP_Base_Sanitizer::enforce_fixed_height().
+	 * Test AMP_Base_Sanitizer::set_layout().
 	 *
-	 * @dataProvider get_enforce_fixed_data
+	 * @dataProvider get_data
 	 * @param array $source_attributes   Source Attrs.
 	 * @param array $expected_attributes Expected Attrs.
 	 * @param array $args                Args.
 	 * @covers AMP_Base_Sanitizer::enforce_fixed_height()
 	 */
-	public function test_enforce_fixed_height( $source_attributes, $expected_attributes, $args = array() ) {
+	public function test_set_layout( $source_attributes, $expected_attributes, $args = array() ) {
 		$sanitizer           = new AMP_Test_Stub_Sanitizer( new DOMDocument(), $args );
-		$returned_attributes = $sanitizer->enforce_fixed_height( $source_attributes );
-
+		$returned_attributes = $sanitizer->set_layout( $source_attributes );
 		$this->assertEquals( $expected_attributes, $returned_attributes );
 	}
 
diff --git a/tests/test-class-amp-comment-walker.php b/tests/test-class-amp-comment-walker.php
new file mode 100644
index 00000000000..1e13edb8c8b
--- /dev/null
+++ b/tests/test-class-amp-comment-walker.php
@@ -0,0 +1,129 @@
+<?php
+/**
+ * Tests for AMP_Comment_Walker class.
+ *
+ * @package AMP
+ */
+
+/**
+ * Tests for AMP_Comment_Walker class.
+ *
+ * @since 0.7
+ */
+class Test_AMP_Comment_Walker extends WP_UnitTestCase {
+
+	/**
+	 * The comment walker.
+	 *
+	 * @var AMP_Comment_Walker
+	 */
+	public $walker;
+
+	/**
+	 * Setup.
+	 *
+	 * @inheritdoc
+	 */
+	public function setUp() {
+		parent::setUp();
+		$this->walker = new AMP_Comment_Walker();
+	}
+
+	/**
+	 * Test AMP_Comment_Walker::start_el.
+	 *
+	 * @covers AMP_Comment_Walker::start_el()
+	 */
+	public function test_start_el() {
+		$GLOBALS['post'] = $this->factory()->post->create(); // WPCS: global override OK.
+		$output          = '<div></div>';
+		$base_args       = array(
+			'format'      => 'baz',
+			'avatar_size' => 100,
+			'max_depth'   => 5,
+		);
+		$args            = array_merge(
+			$base_args,
+			array(
+				'style' => 'baz',
+			)
+		);
+		$comment         = $this->factory()->comment->create_and_get();
+		$this->walker->start_el( $output, $comment, 0, $args );
+		$this->assertContains( '<li data-sort-time=', $output );
+		$this->assertContains( $comment->comment_ID, $output );
+		$this->assertContains( strval( strtotime( $comment->comment_date ) ), $output );
+
+		$output  = '<div></div>';
+		$args    = array_merge(
+			$base_args,
+			array(
+				'style' => 'div',
+			)
+		);
+		$comment = $this->factory()->comment->create_and_get();
+		$this->walker->start_el( $output, $comment, 0, $args );
+		$this->assertContains( '<div data-sort-time=', $output );
+	}
+
+	/**
+	 * Test AMP_Comment_Walker::paged_walk.
+	 *
+	 * @covers AMP_Comment_Walker::paged_walk()
+	 */
+	public function test_paged_walk() {
+		$GLOBALS['post'] = $this->factory()->post->create(); // WPCS: global override OK.
+		$comments        = $this->get_comments();
+		$args            = array(
+			'format'      => 'div',
+			'style'       => 'baz',
+			'avatar_size' => 100,
+			'max_depth'   => 5,
+		);
+		$output          = $this->walker->paged_walk( $comments, 5, 1, 5, $args );
+
+		foreach ( $comments as $comment ) {
+			$this->assertContains( $comment->comment_author, $output );
+			$this->assertContains( $comment->comment_content, $output );
+		}
+	}
+
+	/**
+	 * Test AMP_Comment_Walker::build_thread_latest_date.
+	 *
+	 * @covers AMP_Comment_Walker::build_thread_latest_date()
+	 */
+	public function test_build_thread_latest_date() {
+		$comments      = $this->get_comments();
+		$reflection    = new ReflectionObject( $this->walker );
+		$tested_method = $reflection->getMethod( 'build_thread_latest_date' );
+		$tested_method->setAccessible( true );
+		$latest_time        = $tested_method->invoke( $this->walker, $comments );
+		$comment_thread_age = $reflection->getProperty( 'comment_thread_age' );
+		$comment_thread_age->setAccessible( true );
+		$comment_thread_value = $comment_thread_age->getValue( $this->walker );
+
+		foreach ( $comments as $comment ) {
+			$this->assertEquals( strtotime( $comment->comment_date ), $comment_thread_value[ $comment->comment_ID ] );
+		}
+
+		$last_comment = end( $comments );
+		$this->assertEquals( strtotime( $last_comment->comment_date ), $latest_time );
+	}
+
+	/**
+	 * Gets comments for tests.
+	 *
+	 * @return array $comments An array of WP_Comment instances.
+	 */
+	public function get_comments() {
+		$comments = array();
+		for ( $i = 0; $i < 5; $i++ ) {
+			$comments[] = $this->factory()->comment->create_and_get( array(
+				'comment_date' => gmdate( 'Y-m-d H:i:s', ( time() + $i ) ), // Ensure each comment has a different date.
+			) );
+		}
+		return $comments;
+	}
+
+}
diff --git a/tests/test-class-amp-comments-sanitizer.php b/tests/test-class-amp-comments-sanitizer.php
new file mode 100644
index 00000000000..d5cfda24882
--- /dev/null
+++ b/tests/test-class-amp-comments-sanitizer.php
@@ -0,0 +1,131 @@
+<?php
+/**
+ * Tests for AMP_Comments_Sanitizer class.
+ *
+ * @package AMP
+ */
+
+/**
+ * Tests for AMP_Comments_Sanitizer class.
+ *
+ * @since 0.7
+ */
+class Test_AMP_Comments_Sanitizer extends WP_UnitTestCase {
+
+	/**
+	 * The tested instance.
+	 *
+	 * @var AMP_Comments_Sanitizer
+	 */
+	public $instance;
+
+	/**
+	 * Representation of the DOM.
+	 *
+	 * @var DOMDocument
+	 */
+	public $dom;
+
+	/**
+	 * Setup.
+	 *
+	 * @inheritdoc
+	 */
+	public function setUp() {
+		parent::setUp();
+		$GLOBALS['post'] = $this->factory()->post->create_and_get(); // WPCS: global override ok.
+		$this->dom       = new DOMDocument();
+		$this->instance  = new AMP_Comments_Sanitizer( $this->dom );
+	}
+
+	/**
+	 * Test AMP_Comments_Sanitizer::sanitize.
+	 *
+	 * @covers AMP_Comments_Sanitizer::sanitize()
+	 */
+	public function test_sanitize() {
+		$form = $this->create_form( 'incorrect-action.php' );
+		$this->instance->sanitize();
+		$on = $form->getAttribute( 'on' );
+		$this->assertNotContains( 'submit:AMP.setState(', $on );
+		$this->assertNotContains( 'submit-error:AMP.setState(', $on );
+		foreach ( $this->get_element_names() as $name ) {
+			$this->assertNotContains( $name, $on );
+		}
+
+		// Use an allowed action.
+		$form = $this->create_form( '/wp-comments-post.php' );
+		$this->instance->sanitize();
+		$on = $form->getAttribute( 'on' );
+		$this->assertContains( 'submit:AMP.setState(', $on );
+		$this->assertContains( 'submit-error:AMP.setState(', $on );
+		foreach ( $this->get_element_names() as $name ) {
+			$this->assertContains( $name, $on );
+		}
+	}
+
+	/**
+	 * Test AMP_Comments_Sanitizer::process_comment_form.
+	 *
+	 * @covers AMP_Comments_Sanitizer::process_comment_form()
+	 */
+	public function test_process_comment_form() {
+		$form          = $this->create_form( '/wp-comments-post.php' );
+		$reflection    = new ReflectionObject( $this->instance );
+		$tested_method = $reflection->getMethod( 'process_comment_form' );
+		$tested_method->setAccessible( true );
+		$tested_method->invoke( $this->instance, $form );
+		$on        = $form->getAttribute( 'on' );
+		$amp_state = $this->dom->getElementsByTagName( 'amp-state' )->item( 0 );
+
+		$this->assertContains( 'submit:AMP.setState(', $on );
+		$this->assertContains( 'submit-error:AMP.setState(', $on );
+		$this->assertContains( 'submit-success:AMP.setState(', $on );
+		$this->assertContains( strval( $GLOBALS['post']->ID ), $on );
+		$this->assertEquals( 'script', $amp_state->firstChild->nodeName );
+
+		foreach ( $this->get_element_names() as $name ) {
+			$this->assertContains( $name, $on );
+			$this->assertContains( $name, $amp_state->nodeValue );
+		}
+		foreach ( $form->getElementsByTagName( 'input' ) as $input ) {
+			$on = $input->getAttribute( 'on' );
+			$this->assertContains( 'change:AMP.setState(', $on );
+			$this->assertContains( strval( $GLOBALS['post']->ID ), $on );
+		}
+	}
+
+	/**
+	 * Creates a form for testing.
+	 *
+	 * @param string $action_value Value of the 'action' attribute.
+	 * @return DomElement $form A form element.
+	 */
+	public function create_form( $action_value ) {
+		$form = $this->dom->createElement( 'form' );
+		$this->dom->appendChild( $form );
+		$form->setAttribute( 'action', $action_value );
+
+		foreach ( $this->get_element_names() as $name ) {
+			$element = $this->dom->createElement( 'input' );
+			$element->setAttribute( 'name', $name );
+			$element->setAttribute( 'value', $GLOBALS['post']->ID );
+			$form->appendChild( $element );
+		}
+		return $form;
+	}
+
+	/**
+	 * Gets the element names to add to the <form>.
+	 *
+	 * @return array An array of strings to add to the <form>.
+	 */
+	public function get_element_names() {
+		return array(
+			'comment_post_ID',
+			'foo',
+			'bar',
+		);
+	}
+
+}
diff --git a/tests/test-class-amp-theme-support.php b/tests/test-class-amp-theme-support.php
index 71984f8b8a2..fa9fc2cb42d 100644
--- a/tests/test-class-amp-theme-support.php
+++ b/tests/test-class-amp-theme-support.php
@@ -13,6 +13,13 @@
  */
 class Test_AMP_Theme_Support extends WP_UnitTestCase {
 
+	/**
+	 * The name of the tested class.
+	 *
+	 * @var string
+	 */
+	const TESTED_CLASS = 'AMP_Theme_Support';
+
 	/**
 	 * After a test method runs, reset any state in WordPress the test method might have changed.
 	 *
@@ -28,6 +35,101 @@ public function tearDown() {
 		unset( $_SERVER['REQUEST_URI'] );
 		unset( $_SERVER['REQUEST_METHOD'] );
 		AMP_Response_Headers::$headers_sent = array();
+		if ( isset( $GLOBALS['wp_customize'] ) ) {
+			$GLOBALS['wp_customize']->stop_previewing_theme();
+		}
+	}
+
+	/**
+	 * Test init.
+	 *
+	 * @covers AMP_Theme_Support::init()
+	 * @covers AMP_Theme_Support::finish_init()
+	 */
+	public function test_init() {
+		$_REQUEST['__amp_source_origin'] = 'foo';
+		$_GET['__amp_source_origin']     = 'foo';
+		AMP_Theme_Support::init();
+		$this->assertNotEquals( 10, has_action( 'widgets_init', array( self::TESTED_CLASS, 'register_widgets' ) ) );
+
+		// Ensure that purge_amp_query_vars() didn't execute.
+		$this->assertTrue( isset( $_REQUEST['__amp_source_origin'] ) ); // WPCS: CSRF ok.
+
+		add_theme_support( 'amp' );
+		AMP_Theme_Support::init();
+		$this->assertEquals( 10, has_action( 'widgets_init', array( self::TESTED_CLASS, 'register_widgets' ) ) );
+		$this->assertEquals( PHP_INT_MAX, has_action( 'wp', array( self::TESTED_CLASS, 'finish_init' ) ) );
+		$this->assertFalse( isset( $_REQUEST['__amp_source_origin'] ) ); // WPCS: CSRF ok.
+
+		add_theme_support( 'amp', 'invalid_argumnet_type' );
+		$e = null;
+		try {
+			AMP_Theme_Support::init();
+		} catch ( Exception $exception ) {
+			$e = $exception;
+		}
+		$this->assertInstanceOf( 'PHPUnit_Framework_Error_Notice', $e );
+		$this->assertEquals( 'Expected AMP theme support arg to be array.', $e->getMessage() );
+
+		add_theme_support( 'amp', array(
+			'invalid_param_key' => array(),
+		) );
+		try {
+			AMP_Theme_Support::init();
+		} catch ( Exception $exception ) {
+			$e = $exception;
+		}
+		$this->assertEquals( 'Expected AMP theme support to only have template_dir and/or available_callback.', $e->getMessage() );
+	}
+
+	/**
+	 * Test that amphtml link is added at the right time.
+	 *
+	 * @covers AMP_Theme_Support::finish_init()
+	 */
+	public function test_amphtml_link() {
+		$post_id = $this->factory()->post->create( array( 'post_title' => 'Test' ) );
+		add_theme_support( 'amp', array(
+			'template_dir'       => '...',
+			'available_callback' => function() {
+				return is_singular();
+			},
+		) );
+
+		// Test paired mode singular.
+		remove_action( 'wp_head', 'amp_frontend_add_canonical' );
+		$this->go_to( get_permalink( $post_id ) );
+		AMP_Theme_Support::finish_init();
+		$this->assertEquals( 10, has_action( 'wp_head', 'amp_frontend_add_canonical' ) );
+
+		// Test paired mode homepage.
+		remove_action( 'wp_head', 'amp_frontend_add_canonical' );
+		$this->go_to( home_url() );
+		AMP_Theme_Support::finish_init();
+		$this->assertFalse( has_action( 'wp_head', 'amp_frontend_add_canonical' ) );
+
+		// Test canonical.
+		remove_theme_support( 'amp' );
+		add_theme_support( 'amp' );
+		$this->go_to( get_permalink( $post_id ) );
+		AMP_Theme_Support::finish_init();
+		$this->assertFalse( has_action( 'wp_head', 'amp_frontend_add_canonical' ) );
+	}
+
+	/**
+	 * Test redirect_canonical_amp.
+	 *
+	 * @covers AMP_Theme_Support::redirect_canonical_amp()
+	 */
+	public function test_redirect_canonical_amp() {
+		set_query_var( amp_get_slug(), 1 );
+		try {
+			AMP_Theme_Support::redirect_canonical_amp();
+		} catch ( Exception $exception ) {
+			$e = $exception;
+		}
+		// wp_safe_redirect() modifies the headers, and causes an error.
+		$this->assertTrue( isset( $e ) );
 	}
 
 	/**
@@ -78,138 +180,41 @@ public function test_is_paired_available() {
 	}
 
 	/**
-	 * Test register_widgets().
-	 *
-	 * @covers AMP_Theme_Support::register_widgets()
-	 * @global WP_Widget_Factory $wp_widget_factory
-	 */
-	public function test_register_widgets() {
-		global $wp_widget_factory;
-		remove_all_actions( 'widgets_init' );
-		$wp_widget_factory->widgets = array();
-		wp_widgets_init();
-		AMP_Theme_Support::register_widgets();
-
-		$this->assertArrayNotHasKey( 'WP_Widget_Categories', $wp_widget_factory->widgets );
-		$this->assertArrayHasKey( 'AMP_Widget_Categories', $wp_widget_factory->widgets );
-	}
-
-	/**
-	 * Test amend_comment_form().
+	 * Test is_customize_preview_iframe.
 	 *
-	 * @covers AMP_Theme_Support::amend_comment_form()
+	 * @covers AMP_Theme_Support::is_customize_preview_iframe()
 	 */
-	public function test_amend_comment_form() {
-		$post_id = $this->factory()->post->create();
-		$this->go_to( get_permalink( $post_id ) );
-		$this->assertTrue( is_singular() );
-
-		// Test native AMP.
-		add_theme_support( 'amp' );
-		$this->assertTrue( amp_is_canonical() );
-		ob_start();
-		AMP_Theme_Support::amend_comment_form();
-		$output = ob_get_clean();
-		$this->assertNotContains( '<input type="hidden" name="redirect_to"', $output );
-		$this->assertContains( '<div submit-success>', $output );
-		$this->assertContains( '<div submit-error>', $output );
-
-		// Test paired AMP.
-		add_theme_support( 'amp', array(
-			'template_dir' => 'amp-templates',
+	public function test_is_customize_preview_iframe() {
+		require_once ABSPATH . WPINC . '/class-wp-customize-manager.php';
+		$GLOBALS['wp_customize'] = new WP_Customize_Manager();
+		$this->assertFalse( AMP_Theme_Support::is_customize_preview_iframe() );
+		$GLOBALS['wp_customize'] = new WP_Customize_Manager( array(
+			'messenger_channel' => 'baz',
 		) );
-		$this->assertFalse( amp_is_canonical() );
-		ob_start();
-		AMP_Theme_Support::amend_comment_form();
-		$output = ob_get_clean();
-		$this->assertContains( '<input type="hidden" name="redirect_to"', $output );
-		$this->assertContains( '<div submit-success>', $output );
-		$this->assertContains( '<div submit-error>', $output );
+		$this->assertFalse( AMP_Theme_Support::is_customize_preview_iframe() );
+		$GLOBALS['wp_customize']->start_previewing_theme();
+		$this->assertTrue( AMP_Theme_Support::is_customize_preview_iframe() );
 	}
 
 	/**
-	 * Test prepare_response.
+	 * Test register_paired_hooks.
 	 *
-	 * @global WP_Widget_Factory $wp_widget_factory
-	 * @global WP_Scripts $wp_scripts
-	 * @covers AMP_Theme_Support::prepare_response()
+	 * @covers AMP_Theme_Support::register_paired_hooks()
 	 */
-	public function test_prepare_response() {
-		global $wp_widget_factory, $wp_scripts;
-		$wp_scripts = null;
-
-		add_theme_support( 'amp' );
-		AMP_Theme_Support::init();
-		AMP_Theme_Support::finish_init();
-		$wp_widget_factory = new WP_Widget_Factory();
-		wp_widgets_init();
-
-		add_action( 'wp_enqueue_scripts', function() {
-			wp_enqueue_script( 'amp-list' );
-		} );
-		add_action( 'wp_footer', function() {
-			wp_print_scripts( 'amp-mathml' );
-			?>
-			<amp-mathml layout="container" data-formula="\[x = {-b \pm \sqrt{b^2-4ac} \over 2a}.\]"></amp-mathml>
-			<?php
-		}, 1 );
-
-		ob_start();
-		?>
-		<!DOCTYPE html>
-		<html amp <?php language_attributes(); ?>>
-			<head>
-				<?php wp_head(); ?>
-				<script data-head>document.write('Illegal');</script>
-			</head>
-			<body>
-				<img width="100" height="100" src="https://example.com/test.png">
-				<audio width="400" height="300" src="https://example.com/audios/myaudio.mp3"></audio>
-				<amp-ad type="a9"
-					width="300"
-					height="250"
-					data-aax_size="300x250"
-					data-aax_pubname="test123"
-					data-aax_src="302"></amp-ad>
-				<?php wp_footer(); ?>
-
-				<button onclick="alert('Illegal');">no-onclick</button>
-
-				<style>body { background: black; }</style>
-			</body>
-		</html>
-		<?php
-		$original_html  = trim( ob_get_clean() );
-		$removed_nodes  = array();
-		$sanitized_html = AMP_Theme_Support::prepare_response( $original_html, array(
-			'validation_error_callback' => function( $removed ) use ( &$removed_nodes ) {
-				$removed_nodes[ $removed['node']->nodeName ] = $removed['node'];
-			},
-		) );
-
-		$this->assertContains( '<meta charset="' . get_bloginfo( 'charset' ) . '">', $sanitized_html );
-		$this->assertContains( '<meta name="viewport" content="width=device-width,minimum-scale=1">', $sanitized_html );
-		$this->assertContains( '<style amp-boilerplate>', $sanitized_html );
-		$this->assertContains( '<style amp-custom>body{background:black;}', $sanitized_html );
-		$this->assertContains( '<script type="text/javascript" src="https://cdn.ampproject.org/v0.js" async></script>', $sanitized_html ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedScript
-		$this->assertContains( '<script type="text/javascript" src="https://cdn.ampproject.org/v0/amp-list-latest.js" async custom-element="amp-list"></script>', $sanitized_html ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedScript
-		$this->assertContains( '<script type="text/javascript" src="https://cdn.ampproject.org/v0/amp-mathml-latest.js" async custom-element="amp-mathml"></script>', $sanitized_html ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedScript
-		$this->assertContains( '<meta name="generator" content="AMP Plugin', $sanitized_html );
-
-		$this->assertNotContains( '<img', $sanitized_html );
-		$this->assertContains( '<amp-img', $sanitized_html );
-
-		$this->assertNotContains( '<audio', $sanitized_html );
-		$this->assertContains( '<amp-audio', $sanitized_html );
-
-		// Note these are single-quoted because they are injected after the DOM has been re-serialized, so the type and src attributes come from WP_Scripts::do_item().
-		$this->assertContains( '<script type=\'text/javascript\' src=\'https://cdn.ampproject.org/v0/amp-audio-latest.js\' async custom-element="amp-audio"></script>', $sanitized_html ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedScript
-		$this->assertContains( '<script type=\'text/javascript\' src=\'https://cdn.ampproject.org/v0/amp-ad-latest.js\' async custom-element="amp-ad"></script>', $sanitized_html ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedScript
-
-		$this->assertContains( '<button>no-onclick</button>', $sanitized_html );
-		$this->assertCount( 3, $removed_nodes );
-		$this->assertInstanceOf( 'DOMElement', $removed_nodes['script'] );
-		$this->assertInstanceOf( 'DOMAttr', $removed_nodes['onclick'] );
+	public function test_register_paired_hooks() {
+		$template_types = array(
+			'paged',
+			'index',
+			'404',
+			'archive',
+			'author',
+			'category',
+		);
+		AMP_Theme_Support::register_paired_hooks();
+		foreach ( $template_types as $template_type ) {
+			$this->assertEquals( 10, has_filter( "{$template_type}_template_hierarchy", array( self::TESTED_CLASS, 'filter_paired_template_hierarchy' ) ) );
+		}
+		$this->assertEquals( 100, has_filter( 'template_include', array( self::TESTED_CLASS, 'filter_paired_template_include' ) ) );
 	}
 
 	/**
@@ -252,46 +257,34 @@ public function test_validate_non_amp_theme() {
 	}
 
 	/**
-	 * Test prepare_response for bad/non-HTML.
+	 * Test add_hooks.
 	 *
-	 * @covers AMP_Theme_Support::prepare_response()
+	 * @covers AMP_Theme_Support::add_hooks()
 	 */
-	public function test_prepare_response_bad_html() {
-		add_theme_support( 'amp' );
-		AMP_Theme_Support::init();
-
-		// JSON.
-		$input = '{"success":true}';
-		$this->assertEquals( $input, AMP_Theme_Support::prepare_response( $input ) );
-
-		// Nothing, for redirect.
-		$input = '';
-		$this->assertEquals( $input, AMP_Theme_Support::prepare_response( $input ) );
-
-		// HTML, but very stripped down.
-		$input  = '<html>Hello</html>';
-		$output = AMP_Theme_Support::prepare_response( $input );
-		$this->assertContains( '<html amp', $output );
-	}
-
-	/**
-	 * Test prepare_response to inject html[amp] attribute and ensure HTML5 doctype.
-	 *
-	 * @covers AMP_Theme_Support::prepare_response()
-	 */
-	public function test_prepare_response_to_add_html5_doctype_and_amp_attribute() {
-		add_theme_support( 'amp' );
-		AMP_Theme_Support::init();
-		ob_start();
-		?>
-		<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
-		<html><head><?php wp_head(); ?></head><body><?php wp_footer(); ?></body></html>
-		<?php
-		$original_html  = trim( ob_get_clean() );
-		$sanitized_html = AMP_Theme_Support::prepare_response( $original_html );
-
-		$this->assertStringStartsWith( '<!DOCTYPE html>', $sanitized_html );
-		$this->assertContains( '<html amp', $sanitized_html );
+	public function test_add_hooks() {
+		AMP_Theme_Support::add_hooks();
+		$this->assertFalse( has_action( 'wp_head', 'wp_post_preview_js' ) );
+		$this->assertFalse( has_action( 'wp_head', 'print_emoji_detection_script' ) );
+		$this->assertFalse( has_action( 'wp_print_styles', 'print_emoji_styles' ) );
+		$this->assertFalse( has_action( 'wp_head', 'wp_oembed_add_host_js' ) );
+
+		$this->assertEquals( 0, has_action( 'wp_print_styles', array( self::TESTED_CLASS, 'print_amp_styles' ) ) );
+		$this->assertEquals( 20, has_action( 'wp_head', 'amp_add_generator_metadata' ) );
+		$this->assertEquals( 20, has_action( 'wp_head', 'amp_add_generator_metadata' ) );
+		$this->assertEquals( 10, has_action( 'wp_enqueue_scripts', array( self::TESTED_CLASS, 'enqueue_assets' ) ) );
+
+		$this->assertEquals( 1000, has_action( 'wp_enqueue_scripts', array( self::TESTED_CLASS, 'dequeue_customize_preview_scripts' ) ) );
+		$this->assertEquals( 10, has_filter( 'customize_partial_render', array( self::TESTED_CLASS, 'filter_customize_partial_render' ) ) );
+		$this->assertEquals( 10, has_action( 'wp_footer', 'amp_print_analytics' ) );
+		$this->assertEquals( 100, has_filter( 'show_admin_bar', '__return_false' ) );
+		$this->assertEquals( 0, has_action( 'template_redirect', array( self::TESTED_CLASS, 'start_output_buffering' ) ) );
+
+		$this->assertEquals( PHP_INT_MAX, has_filter( 'wp_list_comments_args', array( self::TESTED_CLASS, 'set_comments_walker' ) ) );
+		$this->assertEquals( 10, has_filter( 'comment_form_defaults', array( self::TESTED_CLASS, 'filter_comment_form_defaults' ) ) );
+		$this->assertEquals( 10, has_filter( 'comment_reply_link', array( self::TESTED_CLASS, 'filter_comment_reply_link' ) ) );
+		$this->assertEquals( 10, has_filter( 'cancel_comment_reply_link', array( self::TESTED_CLASS, 'filter_cancel_comment_reply_link' ) ) );
+		$this->assertEquals( 100, has_action( 'comment_form', array( self::TESTED_CLASS, 'amend_comment_form' ) ) );
+		$this->assertFalse( has_action( 'comment_form', 'wp_comment_form_unfiltered_html_nonce' ) );
 	}
 
 	/**
@@ -300,7 +293,7 @@ public function test_prepare_response_to_add_html5_doctype_and_amp_attribute() {
 	 * @covers AMP_Theme_Support::purge_amp_query_vars()
 	 */
 	public function test_purge_amp_query_vars() {
-		// phpcs:disable WordPress.Security.NonceVerification.NoNonceVerification
+		// phpcs:disable WordPress.CSRF.NonceVerification.NoNonceVerification
 		$bad_query_vars = array(
 			'amp_latest_update_time' => '1517199956',
 			'__amp_source_origin'    => home_url(),
@@ -314,10 +307,10 @@ public function test_purge_amp_query_vars() {
 
 		remove_action( 'wp', 'amp_maybe_add_actions' );
 		$this->go_to( add_query_arg( $all_query_vars, home_url( '/foo/' ) ) );
-		$_REQUEST = $_GET; // phpcs:ignore WordPress.CSRF.NonceVerification.NoNonceVerification
+		$_REQUEST = $_GET;
 		foreach ( $all_query_vars as $key => $value ) {
-			$this->assertArrayHasKey( $key, $_GET ); // phpcs:ignore WordPress.CSRF.NonceVerification.NoNonceVerification
-			$this->assertArrayHasKey( $key, $_REQUEST ); // phpcs:ignore WordPress.CSRF.NonceVerification.NoNonceVerification
+			$this->assertArrayHasKey( $key, $_GET );
+			$this->assertArrayHasKey( $key, $_REQUEST );
 			$this->assertContains( "$key=$value", $_SERVER['QUERY_STRING'] );
 			$this->assertContains( "$key=$value", $_SERVER['REQUEST_URI'] );
 		}
@@ -327,18 +320,18 @@ public function test_purge_amp_query_vars() {
 		$this->assertEqualSets( AMP_Theme_Support::$purged_amp_query_vars, $bad_query_vars );
 
 		foreach ( $bad_query_vars as $key => $value ) {
-			$this->assertArrayNotHasKey( $key, $_GET ); // phpcs:ignore WordPress.CSRF.NonceVerification.NoNonceVerification
-			$this->assertArrayNotHasKey( $key, $_REQUEST ); // phpcs:ignore WordPress.CSRF.NonceVerification.NoNonceVerification
+			$this->assertArrayNotHasKey( $key, $_GET );
+			$this->assertArrayNotHasKey( $key, $_REQUEST );
 			$this->assertNotContains( "$key=$value", $_SERVER['QUERY_STRING'] );
 			$this->assertNotContains( "$key=$value", $_SERVER['REQUEST_URI'] );
 		}
 		foreach ( $ok_query_vars as $key => $value ) {
-			$this->assertArrayHasKey( $key, $_GET ); // phpcs:ignore WordPress.CSRF.NonceVerification.NoNonceVerification
-			$this->assertArrayHasKey( $key, $_REQUEST ); // phpcs:ignore WordPress.CSRF.NonceVerification.NoNonceVerification
+			$this->assertArrayHasKey( $key, $_GET );
+			$this->assertArrayHasKey( $key, $_REQUEST );
 			$this->assertContains( "$key=$value", $_SERVER['QUERY_STRING'] );
 			$this->assertContains( "$key=$value", $_SERVER['REQUEST_URI'] );
 		}
-		// phpcs:enable WordPress.Security.NonceVerification.NoNonceVerification
+		// phpcs:enable WordPress.CSRF.NonceVerification.NoNonceVerification
 	}
 
 	/**
@@ -468,7 +461,7 @@ public function test_handle_wp_die() {
 	public function test_intercept_post_request_redirect() {
 
 		add_theme_support( 'amp' );
-		$url = home_url( '/', 'https' );
+		$url = home_url( '', 'https' ) . ':443/?test=true#test';
 
 		add_filter( 'wp_doing_ajax', '__return_true' );
 		add_filter( 'wp_die_ajax_handler', function () {
@@ -571,6 +564,248 @@ public function test_intercept_post_request_redirect() {
 		);
 	}
 
+	/**
+	 * Test register_widgets().
+	 *
+	 * @covers AMP_Theme_Support::register_widgets()
+	 * @global WP_Widget_Factory $wp_widget_factory
+	 */
+	public function test_register_widgets() {
+		global $wp_widget_factory;
+		remove_all_actions( 'widgets_init' );
+		$wp_widget_factory->widgets = array();
+		wp_widgets_init();
+		AMP_Theme_Support::register_widgets();
+
+		$this->assertArrayNotHasKey( 'WP_Widget_Categories', $wp_widget_factory->widgets );
+		$this->assertArrayHasKey( 'AMP_Widget_Categories', $wp_widget_factory->widgets );
+	}
+
+	/**
+	 * Test register_content_embed_handlers.
+	 *
+	 * @covers AMP_Theme_Support::register_content_embed_handlers()
+	 */
+	public function test_register_content_embed_handlers() {
+		$embed_handlers = AMP_Theme_Support::register_content_embed_handlers();
+		foreach ( $embed_handlers as $embed_handler ) {
+			$this->assertTrue( is_subclass_of( $embed_handler, 'AMP_Base_Embed_Handler' ) );
+			$reflection = new ReflectionObject( $embed_handler );
+			$args       = $reflection->getProperty( 'args' );
+			$args->setAccessible( true );
+			$property = $args->getValue( $embed_handler );
+			$this->assertEquals( AMP_Post_Template::CONTENT_MAX_WIDTH, $property['content_max_width'] );
+		}
+	}
+
+	/**
+	 * Test set_comments_walker.
+	 *
+	 * @covers AMP_Theme_Support::set_comments_walker()
+	 */
+	public function test_set_comments_walker() {
+		$args = AMP_Theme_Support::set_comments_walker( array(
+			'walker' => null,
+		) );
+		$this->assertInstanceOf( 'AMP_Comment_Walker', $args['walker'] );
+	}
+
+	/**
+	 * Test amend_comment_form().
+	 *
+	 * @covers AMP_Theme_Support::amend_comment_form()
+	 */
+	public function test_amend_comment_form() {
+		$post_id = $this->factory()->post->create();
+		$this->go_to( get_permalink( $post_id ) );
+		$this->assertTrue( is_singular() );
+
+		// Test native AMP.
+		add_theme_support( 'amp' );
+		$this->assertTrue( amp_is_canonical() );
+		ob_start();
+		AMP_Theme_Support::amend_comment_form();
+		$output = ob_get_clean();
+		$this->assertNotContains( '<input type="hidden" name="redirect_to"', $output );
+		$this->assertContains( '<div submit-success>', $output );
+		$this->assertContains( '<div submit-error>', $output );
+
+		// Test paired AMP.
+		add_theme_support( 'amp', array(
+			'template_dir' => 'amp-templates',
+		) );
+		$this->assertFalse( amp_is_canonical() );
+		ob_start();
+		AMP_Theme_Support::amend_comment_form();
+		$output = ob_get_clean();
+		$this->assertContains( '<input type="hidden" name="redirect_to"', $output );
+		$this->assertContains( '<div submit-success>', $output );
+		$this->assertContains( '<div submit-error>', $output );
+	}
+
+	/**
+	 * Test filter_paired_template_hierarchy.
+	 *
+	 * @covers AMP_Theme_Support::filter_paired_template_hierarchy()
+	 */
+	public function test_filter_paired_template_hierarchy() {
+		$template_dir = 'amp-templates';
+		add_theme_support( 'amp', array(
+			'template_dir' => $template_dir,
+		) );
+		$templates          = array(
+			'single-post-example.php',
+			'single-post.php',
+			'single.php',
+		);
+		$filtered_templates = AMP_Theme_Support::filter_paired_template_hierarchy( $templates );
+		foreach ( $filtered_templates as $key => $filtered_template ) {
+			$this->assertEquals( $template_dir . '/' . $templates[ $key ], $filtered_template );
+		}
+	}
+
+	/**
+	 * Test filter_paired_template_include.
+	 *
+	 * @covers AMP_Theme_Support::filter_paired_template_include()
+	 */
+	public function test_filter_paired_template_include() {
+		$template_dir = 'amp-templates';
+		$template     = 'single.php';
+		add_theme_support( 'amp', array(
+			'template_dir' => $template_dir,
+		) );
+		$this->assertEquals( $template, AMP_Theme_Support::filter_paired_template_include( $template ) );
+		remove_theme_support( 'amp' );
+		try {
+			AMP_Theme_Support::filter_paired_template_include( $template );
+		} catch ( Exception $exception ) {
+			$e = $exception;
+		}
+		$this->assertTrue( isset( $e ) );
+	}
+
+	/**
+	 * Test get_current_canonical_url.
+	 *
+	 * @covers AMP_Theme_Support::get_current_canonical_url()
+	 */
+	public function test_get_current_canonical_url() {
+		global $post, $wp;
+		$home_url = home_url( '/' );
+		$this->assertEquals( $home_url, AMP_Theme_Support::get_current_canonical_url() );
+
+		$added_query_vars = array(
+			'foo' => 'bar',
+		);
+		$wp->query_vars   = $added_query_vars;
+		$this->assertEquals( add_query_arg( $added_query_vars, $home_url ), AMP_Theme_Support::get_current_canonical_url() );
+
+		$post = $this->factory()->post->create_and_get(); // WPCS: global override ok.
+		$this->go_to( get_permalink( $post ) );
+		$this->assertEquals( wp_get_canonical_url(), AMP_Theme_Support::get_current_canonical_url() );
+
+	}
+
+	/**
+	 * Test get_comment_form_state_id.
+	 *
+	 * @covers AMP_Theme_Support::get_comment_form_state_id()
+	 */
+	public function test_get_comment_form_state_id() {
+		$post_id = 54;
+		$this->assertEquals( 'commentform_post_' . $post_id, AMP_Theme_Support::get_comment_form_state_id( $post_id ) );
+		$post_id = 91542;
+		$this->assertEquals( 'commentform_post_' . $post_id, AMP_Theme_Support::get_comment_form_state_id( $post_id ) );
+	}
+
+	/**
+	 * Test filter_comment_form_defaults.
+	 *
+	 * @covers AMP_Theme_Support::filter_comment_form_defaults()
+	 */
+	public function test_filter_comment_form_defaults() {
+		global $post;
+		$post     = $this->factory()->post->create_and_get(); // WPCS: global override ok.
+		$defaults = AMP_Theme_Support::filter_comment_form_defaults( array(
+			'title_reply_to'      => 'Reply To',
+			'title_reply'         => 'Reply',
+			'cancel_reply_before' => '',
+			'title_reply_before'  => '',
+		) );
+		$this->assertContains( AMP_Theme_Support::get_comment_form_state_id( get_the_ID() ), $defaults['title_reply_before'] );
+		$this->assertContains( 'replyToName ?', $defaults['title_reply_before'] );
+		$this->assertContains( '</span>', $defaults['cancel_reply_before'] );
+	}
+
+	/**
+	 * Test filter_comment_reply_link.
+	 *
+	 * @covers AMP_Theme_Support::filter_comment_reply_link()
+	 */
+	public function test_filter_comment_reply_link() {
+		global $post;
+		$post          = $this->factory()->post->create_and_get(); // WPCS: global override ok.
+		$comment       = $this->factory()->comment->create_and_get();
+		$link          = get_comment_link( $comment );
+		$respond_id    = '5234';
+		$reply_text    = 'Reply';
+		$reply_to_text = 'Reply to';
+		$args          = compact( 'respond_id', 'reply_text', 'reply_to_text' );
+		$comment       = $this->factory()->comment->create_and_get();
+		update_option( 'comment_registration', true );
+		$filtered_link = AMP_Theme_Support::filter_comment_reply_link( $link, $args, $comment );
+		$this->assertEquals( $link, $filtered_link );
+		update_option( 'comment_registration', false );
+
+		$filtered_link = AMP_Theme_Support::filter_comment_reply_link( $link, $args, $comment );
+		$this->assertContains( AMP_Theme_Support::get_comment_form_state_id( get_the_ID() ), $filtered_link );
+		$this->assertContains( $comment->comment_author, $filtered_link );
+		$this->assertContains( $comment->comment_ID, $filtered_link );
+		$this->assertContains( 'tap:AMP.setState', $filtered_link );
+		$this->assertContains( $reply_text, $filtered_link );
+		$this->assertContains( $reply_to_text, $filtered_link );
+		$this->assertContains( $respond_id, $filtered_link );
+	}
+
+	/**
+	 * Test filter_cancel_comment_reply_link.
+	 *
+	 * @covers AMP_Theme_Support::filter_cancel_comment_reply_link()
+	 */
+	public function test_filter_cancel_comment_reply_link() {
+		global $post;
+		$post                   = $this->factory()->post->create_and_get(); // WPCS: global override ok.
+		$url                    = get_permalink( $post );
+		$_SERVER['REQUEST_URI'] = $url;
+		$this->factory()->comment->create_and_get();
+		$formatted_link = get_cancel_comment_reply_link();
+		$link           = remove_query_arg( 'replytocom' );
+		$text           = 'Cancel your reply';
+		$filtered_link  = AMP_Theme_Support::filter_cancel_comment_reply_link( $formatted_link, $link, $text );
+		$this->assertContains( $url, $filtered_link );
+		$this->assertContains( $text, $filtered_link );
+		$this->assertContains( '<a id="cancel-comment-reply-link"', $filtered_link );
+		$this->assertContains( '.values.comment_parent ==', $filtered_link );
+		$this->assertContains( 'tap:AMP.setState(', $filtered_link );
+
+		$filtered_link_no_text_passed = AMP_Theme_Support::filter_cancel_comment_reply_link( $formatted_link, $link, '' );
+		$this->assertContains( 'Click here to cancel reply.', $filtered_link_no_text_passed );
+	}
+
+	/**
+	 * Test print_amp_styles.
+	 *
+	 * @covers AMP_Theme_Support::print_amp_styles()
+	 */
+	public function test_print_amp_styles() {
+		ob_start();
+		AMP_Theme_Support::print_amp_styles();
+		$output = ob_get_clean();
+		$this->assertContains( amp_get_boilerplate_code(), $output );
+		$this->assertContains( '<style amp-custom></style>', $output );
+	}
+
 	/**
 	 * Test ensure_required_markup().
 	 *
@@ -587,6 +822,234 @@ public function test_ensure_required_markup( $script, $expected ) {
 		$this->assertEquals( $expected, substr_count( $dom->saveHTML(), 'schema.org' ) );
 	}
 
+	/**
+	 * Test dequeue_customize_preview_scripts.
+	 *
+	 * @covers AMP_Theme_Support::dequeue_customize_preview_scripts()
+	 */
+	public function test_dequeue_customize_preview_scripts() {
+		// Ensure AMP_Theme_Support::is_customize_preview_iframe() is true.
+		require_once ABSPATH . WPINC . '/class-wp-customize-manager.php';
+		$GLOBALS['wp_customize'] = new WP_Customize_Manager( array(
+			'messenger_channel' => 'baz',
+		) );
+		$GLOBALS['wp_customize']->start_previewing_theme();
+		$customize_preview = 'customize-preview';
+		$preview_style     = 'example-preview-style';
+		wp_enqueue_style( $preview_style, home_url( '/' ), array( $customize_preview ) );
+		AMP_Theme_Support::dequeue_customize_preview_scripts();
+		$this->assertTrue( wp_style_is( $preview_style ) );
+		$this->assertTrue( wp_style_is( $customize_preview ) );
+
+		wp_enqueue_style( $preview_style, home_url( '/' ), array( $customize_preview ) );
+		wp_enqueue_style( $customize_preview );
+		// Ensure AMP_Theme_Support::is_customize_preview_iframe() is false.
+		$GLOBALS['wp_customize'] = new WP_Customize_Manager();
+		AMP_Theme_Support::dequeue_customize_preview_scripts();
+		$this->assertFalse( wp_style_is( $preview_style ) );
+		$this->assertFalse( wp_style_is( $customize_preview ) );
+	}
+
+	/**
+	 * Test start_output_buffering.
+	 *
+	 * @covers AMP_Theme_Support::start_output_buffering()
+	 */
+	public function test_start_output_buffering() {
+		if ( ! function_exists( 'newrelic_disable_autorum ' ) ) {
+			/**
+			 * Define newrelic_disable_autorum to allow passing line.
+			 */
+			function newrelic_disable_autorum() {
+				return true;
+			}
+		}
+
+		add_theme_support( 'amp' );
+		AMP_Theme_Support::init();
+		AMP_Theme_Support::finish_init();
+
+		$ob_level = ob_get_level();
+		AMP_Theme_Support::start_output_buffering();
+
+		$this->assertEquals( 0, has_action( 'shutdown', array( self::TESTED_CLASS, 'finish_output_buffering' ) ) );
+		$this->assertTrue( ob_get_level() > $ob_level );
+		// End output buffer.
+		if ( ob_get_level() > $ob_level ) {
+			ob_get_clean();
+		}
+	}
+
+	/**
+	 * Test finish_output_buffering.
+	 *
+	 * @covers AMP_Theme_Support::finish_output_buffering()
+	 */
+	public function test_finish_output_buffering() {
+		add_theme_support( 'amp' );
+		AMP_Theme_Support::init();
+		AMP_Theme_Support::finish_init();
+
+		// start first layer buffer.
+		ob_start();
+		AMP_Theme_Support::start_output_buffering();
+		echo '<img src="test.png"><script data-test>document.write(\'Illegal\');</script>';
+		AMP_Theme_Support::finish_output_buffering();
+		// get first layer buffer.
+		$output = ob_get_clean();
+
+		$this->assertContains( '<html amp', $output );
+		$this->assertContains( '<amp-img src="test.png"', $output );
+		$this->assertNotContains( '<script data-test', $output );
+
+	}
+
+	/**
+	 * Test filter_customize_partial_render.
+	 *
+	 * @covers AMP_Theme_Support::filter_customize_partial_render()
+	 */
+	public function test_filter_customize_partial_render() {
+		add_theme_support( 'amp' );
+		AMP_Theme_Support::init();
+		AMP_Theme_Support::finish_init();
+
+		$partial = '<img src="test.png"><script data-head>document.write(\'Illegal\');</script>';
+		$output  = AMP_Theme_Support::filter_customize_partial_render( $partial );
+		$this->assertContains( '<amp-img src="test.png"', $output );
+		$this->assertNotContains( '<script', $output );
+		$this->assertNotContains( '<html', $output );
+	}
+
+	/**
+	 * Test prepare_response.
+	 *
+	 * @global WP_Widget_Factory $wp_widget_factory
+	 * @global WP_Scripts $wp_scripts
+	 * @covers AMP_Theme_Support::prepare_response()
+	 */
+	public function test_prepare_response() {
+		global $wp_widget_factory, $wp_scripts, $wp_styles;
+		$wp_scripts = null;
+		$wp_styles  = null;
+
+		add_theme_support( 'amp' );
+		AMP_Theme_Support::init();
+		AMP_Theme_Support::finish_init();
+		$wp_widget_factory = new WP_Widget_Factory();
+		wp_widgets_init();
+
+		add_action( 'wp_enqueue_scripts', function() {
+			wp_enqueue_script( 'amp-list' );
+		} );
+		add_action( 'wp_footer', function() {
+			wp_print_scripts( 'amp-mathml' );
+			?>
+			<amp-mathml layout="container" data-formula="\[x = {-b \pm \sqrt{b^2-4ac} \over 2a}.\]"></amp-mathml>
+			<?php
+		}, 1 );
+
+		ob_start();
+		?>
+		<!DOCTYPE html>
+		<html amp <?php language_attributes(); ?>>
+			<head>
+				<?php wp_head(); ?>
+				<script data-head>document.write('Illegal');</script>
+			</head>
+			<body>
+				<img width="100" height="100" src="https://example.com/test.png">
+				<audio width="400" height="300" src="https://example.com/audios/myaudio.mp3"></audio>
+				<amp-ad type="a9"
+					width="300"
+					height="250"
+					data-aax_size="300x250"
+					data-aax_pubname="test123"
+					data-aax_src="302"></amp-ad>
+				<?php wp_footer(); ?>
+
+				<button onclick="alert('Illegal');">no-onclick</button>
+
+				<style>body { background: black; }</style>
+			</body>
+		</html>
+		<?php
+		$original_html  = trim( ob_get_clean() );
+		$removed_nodes  = array();
+		$sanitized_html = AMP_Theme_Support::prepare_response( $original_html, array(
+			'validation_error_callback' => function( $removed ) use ( &$removed_nodes ) {
+				$removed_nodes[ $removed['node']->nodeName ] = $removed['node'];
+			},
+		) );
+
+		$this->assertContains( '<meta charset="' . get_bloginfo( 'charset' ) . '">', $sanitized_html );
+		$this->assertContains( '<meta name="viewport" content="width=device-width,minimum-scale=1">', $sanitized_html );
+		$this->assertContains( '<style amp-boilerplate>', $sanitized_html );
+		$this->assertContains( '<style amp-custom>body{background:black;}', $sanitized_html );
+		$this->assertContains( '<script type="text/javascript" src="https://cdn.ampproject.org/v0.js" async></script>', $sanitized_html ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedScript
+		$this->assertContains( '<script type="text/javascript" src="https://cdn.ampproject.org/v0/amp-list-latest.js" async custom-element="amp-list"></script>', $sanitized_html ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedScript
+		$this->assertContains( '<script type="text/javascript" src="https://cdn.ampproject.org/v0/amp-mathml-latest.js" async custom-element="amp-mathml"></script>', $sanitized_html ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedScript
+		$this->assertContains( '<meta name="generator" content="AMP Plugin', $sanitized_html );
+
+		$this->assertNotContains( '<img', $sanitized_html );
+		$this->assertContains( '<amp-img', $sanitized_html );
+
+		$this->assertNotContains( '<audio', $sanitized_html );
+		$this->assertContains( '<amp-audio', $sanitized_html );
+
+		// Note these are single-quoted because they are injected after the DOM has been re-serialized, so the type and src attributes come from WP_Scripts::do_item().
+		$this->assertContains( '<script type=\'text/javascript\' src=\'https://cdn.ampproject.org/v0/amp-audio-latest.js\' async custom-element="amp-audio"></script>', $sanitized_html ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedScript
+		$this->assertContains( '<script type=\'text/javascript\' src=\'https://cdn.ampproject.org/v0/amp-ad-latest.js\' async custom-element="amp-ad"></script>', $sanitized_html ); // phpcs:ignore WordPress.WP.EnqueuedResources.NonEnqueuedScript
+
+		$this->assertContains( '<button>no-onclick</button>', $sanitized_html );
+		$this->assertCount( 3, $removed_nodes );
+		$this->assertInstanceOf( 'DOMElement', $removed_nodes['script'] );
+		$this->assertInstanceOf( 'DOMAttr', $removed_nodes['onclick'] );
+	}
+
+	/**
+	 * Test prepare_response for bad/non-HTML.
+	 *
+	 * @covers AMP_Theme_Support::prepare_response()
+	 */
+	public function test_prepare_response_bad_html() {
+		add_theme_support( 'amp' );
+		AMP_Theme_Support::init();
+
+		// JSON.
+		$input = '{"success":true}';
+		$this->assertEquals( $input, AMP_Theme_Support::prepare_response( $input ) );
+
+		// Nothing, for redirect.
+		$input = '';
+		$this->assertEquals( $input, AMP_Theme_Support::prepare_response( $input ) );
+
+		// HTML, but very stripped down.
+		$input  = '<html>Hello</html>';
+		$output = AMP_Theme_Support::prepare_response( $input );
+		$this->assertContains( '<html amp', $output );
+	}
+
+	/**
+	 * Test prepare_response to inject html[amp] attribute and ensure HTML5 doctype.
+	 *
+	 * @covers AMP_Theme_Support::prepare_response()
+	 */
+	public function test_prepare_response_to_add_html5_doctype_and_amp_attribute() {
+		add_theme_support( 'amp' );
+		AMP_Theme_Support::init();
+		ob_start();
+		?>
+		<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+		<html><head><?php wp_head(); ?></head><body><?php wp_footer(); ?></body></html>
+		<?php
+		$original_html  = trim( ob_get_clean() );
+		$sanitized_html = AMP_Theme_Support::prepare_response( $original_html );
+
+		$this->assertStringStartsWith( '<!DOCTYPE html>', $sanitized_html );
+		$this->assertContains( '<html amp', $sanitized_html );
+	}
+
 	/**
 	 * Data provider for test_ensure_required_markup.
 	 *
@@ -627,4 +1090,38 @@ public function test_enqueue_assets() {
 		$this->assertTrue( in_array( $script_slug, wp_scripts()->queue, true ) );
 		$this->assertTrue( in_array( $style_slug, wp_styles()->queue, true ) );
 	}
+
+	/**
+	 * Test AMP_Theme_Support::whitelist_layout_in_wp_kses_allowed_html().
+	 *
+	 * @see AMP_Theme_Support::whitelist_layout_in_wp_kses_allowed_html()
+	 */
+	public function test_whitelist_layout_in_wp_kses_allowed_html() {
+		$attribute             = 'data-amp-layout';
+		$image_no_dimensions   = array(
+			'img' => array(
+				$attribute => true,
+			),
+		);
+		$image_with_dimensions = array_merge(
+			$image_no_dimensions,
+			array(
+				'height' => '100',
+				'width'  => '100',
+			)
+		);
+
+		$this->assertEquals( array(), AMP_Theme_Support::whitelist_layout_in_wp_kses_allowed_html( array() ) );
+		$this->assertEquals( $image_no_dimensions, AMP_Theme_Support::whitelist_layout_in_wp_kses_allowed_html( $image_no_dimensions ) );
+
+		$context = AMP_Theme_Support::whitelist_layout_in_wp_kses_allowed_html( $image_with_dimensions );
+		$this->assertTrue( $context['img'][ $attribute ] );
+
+		$context = AMP_Theme_Support::whitelist_layout_in_wp_kses_allowed_html( $image_with_dimensions );
+		$this->assertTrue( $context['img'][ $attribute ] );
+
+		add_filter( 'wp_kses_allowed_html', 'AMP_Theme_Support::whitelist_layout_in_wp_kses_allowed_html', 10, 2 );
+		$image = '<img data-amp-layout="fill">';
+		$this->assertEquals( $image, wp_kses_post( $image ) );
+	}
 }
diff --git a/tests/test-class-amp-validation-utils.php b/tests/test-class-amp-validation-utils.php
index 6217f7c9323..f8c4b82f156 100644
--- a/tests/test-class-amp-validation-utils.php
+++ b/tests/test-class-amp-validation-utils.php
@@ -94,6 +94,7 @@ public function setUp() {
 	 */
 	public function tearDown() {
 		$GLOBALS['wp_registered_widgets'] = $this->original_wp_registered_widgets; // WPCS: override ok.
+		unset( $GLOBALS['current_screen'] );
 		parent::tearDown();
 	}
 
@@ -114,6 +115,7 @@ public function test_init() {
 		$this->assertEquals( 10, has_filter( 'bulk_actions-edit-' . AMP_Validation_Utils::POST_TYPE_SLUG, self::TESTED_CLASS . '::add_bulk_action' ) );
 		$this->assertEquals( 10, has_filter( 'handle_bulk_actions-edit-' . AMP_Validation_Utils::POST_TYPE_SLUG, self::TESTED_CLASS . '::handle_bulk_action' ) );
 		$this->assertEquals( 10, has_action( 'admin_notices', self::TESTED_CLASS . '::remaining_error_notice' ) );
+		$this->assertEquals( 10, has_action( 'admin_notices', self::TESTED_CLASS . '::persistent_object_caching_notice' ) );
 		$this->assertEquals( 10, has_action( 'admin_menu', self::TESTED_CLASS . '::remove_publish_meta_box' ) );
 		$this->assertEquals( 10, has_action( 'add_meta_boxes', self::TESTED_CLASS . '::add_meta_boxes' ) );
 	}
@@ -1359,4 +1361,37 @@ public function get_mock_errors() {
 		);
 	}
 
+	/**
+	 * Test for persistent_object_caching_notice()
+	 *
+	 * @covers AMP_Validation_Utils::persistent_object_caching_notice()
+	 */
+	public function test_persistent_object_caching_notice() {
+		set_current_screen( 'toplevel_page_amp-options' );
+		$text = 'The AMP plugin performs at its best when persistent object cache is enabled.';
+
+		wp_using_ext_object_cache( null );
+		ob_start();
+		AMP_Validation_Utils::persistent_object_caching_notice();
+		$this->assertContains( $text, ob_get_clean() );
+
+		wp_using_ext_object_cache( true );
+		ob_start();
+		AMP_Validation_Utils::persistent_object_caching_notice();
+		$this->assertNotContains( $text, ob_get_clean() );
+
+		set_current_screen( 'edit.php' );
+
+		wp_using_ext_object_cache( null );
+		ob_start();
+		AMP_Validation_Utils::persistent_object_caching_notice();
+		$this->assertNotContains( $text, ob_get_clean() );
+
+		wp_using_ext_object_cache( true );
+		ob_start();
+		AMP_Validation_Utils::persistent_object_caching_notice();
+		$this->assertNotContains( $text, ob_get_clean() );
+
+	}
+
 }
diff --git a/tests/test-tag-and-attribute-sanitizer.php b/tests/test-tag-and-attribute-sanitizer.php
index c99416d81b1..5d30dca97f4 100644
--- a/tests/test-tag-and-attribute-sanitizer.php
+++ b/tests/test-tag-and-attribute-sanitizer.php
@@ -721,6 +721,24 @@ public function get_body_data() {
 				null, // No change.
 				array( 'amp-selector', 'amp-form', 'amp-carousel' ),
 			),
+
+			'amp_live_list_sort'                                        => array(
+				'<amp-live-list sort="ascending" data-poll-interval="15000" data-max-items-per-page="5" id="amp-live-list-insert-blog"><button update on="tap:amp-live-list-insert-blog.update" class="ampstart-btn ml1 caps">You have updates</button><div items><div id="A green landscape with trees." data-sort-time="20180317225019">Hello</div></div></amp-live-list>',
+				null, // No change.
+				array( 'amp-live-list' ),
+			),
+
+			'amp_consent'                                               => array(
+				'<amp-consent media="all" noloading></amp-consent>',
+				null, // No change.
+				array( 'amp-consent' ),
+			),
+
+			'amp_date_picker'                                           => array(
+				'<amp-date-picker id="simple-date-picker" type="single" mode="overlay" layout="container" on="select:AMP.setState({date1: event.date, dateType1: event.id})" format="Y-MM-DD" open-after-select input-selector="[name=date1]" class="mr1 ml1 flex picker"><div class="ampstart-input inline-block mt1"><input class="border-none p0" name="date1" placeholder="Pick a date"></div><button class="ampstart-btn m1 caps" on="tap: simple-date-picker.clear">Clear</button></amp-date-picker>',
+				null, // No change.
+				array( 'amp-date-picker' ),
+			),
 		);
 	}
 
diff --git a/wpcom-helper.php b/wpcom-helper.php
index eddc6ef2890..36f931107d3 100644
--- a/wpcom-helper.php
+++ b/wpcom-helper.php
@@ -1,17 +1,22 @@
 <?php
+/**
+ * WPCOM-specific things.
+ *
+ * @todo Move this into Jetpack. See https://github.com/Automattic/amp-wp/issues/1021
+ * @package AMP
+ */
 
-// WPCOM-specific things
 add_action( 'pre_amp_render_post', 'jetpack_amp_disable_the_content_filters' );
 
-// Disable admin menu
+// Disable admin menu.
 add_filter( 'amp_options_menu_is_enabled', '__return_false', 9999 );
 
 /**
  * Disable the_content filters for Jetpack.
  *
- * @param int $post_id Post ID.
+ * @since 0.3
  */
-function jetpack_amp_disable_the_content_filters( $post_id ) {
+function jetpack_amp_disable_the_content_filters() {
 	add_filter( 'post_flair_disable', '__return_true', 99 );
 	add_filter( 'videopress_show_2015_player', '__return_true' );
 	add_filter( 'protected_embeds_use_form_post', '__return_false' );
@@ -24,7 +29,12 @@ function jetpack_amp_disable_the_content_filters( $post_id ) {
 
 add_action( 'amp_post_template_head', 'jetpack_amp_add_og_tags' );
 
-function jetpack_amp_add_og_tags( $amp_template ) {
+/**
+ * Add Open Graph tags.
+ *
+ * @since 0.3
+ */
+function jetpack_amp_add_og_tags() {
 	if ( function_exists( 'jetpack_og_tags' ) ) {
 		jetpack_og_tags();
 	}
@@ -32,9 +42,18 @@ function jetpack_amp_add_og_tags( $amp_template ) {
 
 add_filter( 'amp_post_template_metadata', 'jetpack_amp_post_template_metadata', 10, 2 );
 
+/**
+ * Add publisher and image metadata.
+ *
+ * @since 0.3
+ *
+ * @param array   $metadata Metadata array.
+ * @param WP_Post $post     Post.
+ * @return array Modified metadata array.
+ */
 function jetpack_amp_post_template_metadata( $metadata, $post ) {
 	if ( isset( $metadata['publisher'] ) && ! isset( $metadata['publisher']['logo'] ) ) {
-		$metadata = wpcom_amp_add_blavatar_to_metadata( $metadata, $post );
+		$metadata = wpcom_amp_add_blavatar_to_metadata( $metadata );
 	}
 
 	if ( ! isset( $metadata['image'] ) ) {
@@ -44,22 +63,40 @@ function jetpack_amp_post_template_metadata( $metadata, $post ) {
 	return $metadata;
 }
 
-function wpcom_amp_add_blavatar_to_metadata( $metadata, $post ) {
+/**
+ * Add blavatar to metadata.
+ *
+ * @since 0.3
+ *
+ * @param array $metadata Metadata.
+ * @return array Metadata.
+ */
+function wpcom_amp_add_blavatar_to_metadata( $metadata ) {
 	if ( ! function_exists( 'blavatar_domain' ) ) {
 		return $metadata;
 	}
 
 	$size = 60;
+
 	$metadata['publisher']['logo'] = array(
-		'@type' => 'ImageObject',
-		'url' => blavatar_url( blavatar_domain( site_url() ), 'img', $size, staticize_subdomain( 'https://wordpress.com/i/favicons/apple-touch-icon-60x60.png' ) ),
-		'width' => $size,
+		'@type'  => 'ImageObject',
+		'url'    => blavatar_url( blavatar_domain( site_url() ), 'img', $size, staticize_subdomain( 'https://wordpress.com/i/favicons/apple-touch-icon-60x60.png' ) ),
+		'width'  => $size,
 		'height' => $size,
 	);
 
 	return $metadata;
 }
 
+/**
+ * Add image to metadata.
+ *
+ * @since 0.3.2
+ *
+ * @param array   $metadata Metadata.
+ * @param WP_Post $post     Post.
+ * @return array Metadata.
+ */
 function wpcom_amp_add_image_to_metadata( $metadata, $post ) {
 	if ( ! class_exists( 'Jetpack_PostImages' ) ) {
 		return wpcom_amp_add_fallback_image_to_metadata( $metadata );
@@ -67,10 +104,10 @@ function wpcom_amp_add_image_to_metadata( $metadata, $post ) {
 
 	$image = Jetpack_PostImages::get_image( $post->ID, array(
 		'fallback_to_avatars' => true,
-		'avatar_size' => 200,
-		// AMP already attempts these
-		'from_thumbnail' => false,
-		'from_attachment' => false,
+		'avatar_size'         => 200,
+		// AMP already attempts these.
+		'from_thumbnail'      => false,
+		'from_attachment'     => false,
 	) );
 
 	if ( empty( $image ) ) {
@@ -80,30 +117,37 @@ function wpcom_amp_add_image_to_metadata( $metadata, $post ) {
 	if ( ! isset( $image['src_width'] ) ) {
 		$dimensions = wpcom_amp_extract_image_dimensions_from_getimagesize( array(
 			$image['src'] => false,
-			)
-		);
+		) );
 
 		if ( false !== $dimensions[ $image['src'] ] ) {
-			$image['src_width'] = $dimensions['width'];
+			$image['src_width']  = $dimensions['width'];
 			$image['src_height'] = $dimensions['height'];
 		}
 	}
 
 	$metadata['image'] = array(
-		'@type' => 'ImageObject',
-		'url' => $image['src'],
-		'width' => $image['src_width'],
+		'@type'  => 'ImageObject',
+		'url'    => $image['src'],
+		'width'  => $image['src_width'],
 		'height' => $image['src_height'],
 	);
 
 	return $metadata;
 }
 
+/**
+ * Add fallback image to metadata.
+ *
+ * @since 0.3.2
+ *
+ * @param array $metadata Metadata.
+ * @return array Metadata.
+ */
 function wpcom_amp_add_fallback_image_to_metadata( $metadata ) {
 	$metadata['image'] = array(
-		'@type' => 'ImageObject',
-		'url' => staticize_subdomain( 'https://wordpress.com/i/blank.jpg' ),
-		'width' => 200,
+		'@type'  => 'ImageObject',
+		'url'    => staticize_subdomain( 'https://wordpress.com/i/blank.jpg' ),
+		'width'  => 200,
 		'height' => 200,
 	);
 
@@ -111,19 +155,33 @@ function wpcom_amp_add_fallback_image_to_metadata( $metadata ) {
 }
 
 add_action( 'amp_extract_image_dimensions_batch_callbacks_registered', 'wpcom_amp_extract_image_dimensions_batch_add_custom_callbacks' );
+
+/**
+ * Add hooks to extract image dimensions.
+ *
+ * @since 0.5
+ */
 function wpcom_amp_extract_image_dimensions_batch_add_custom_callbacks() {
 	// If images are being served from Photon or WP.com files, try extracting the size using querystring.
 	add_action( 'amp_extract_image_dimensions_batch', 'wpcom_amp_extract_image_dimensions_from_querystring', 9, 1 ); // Hook in before the default extractors.
 
 	// Uses a special wpcom lib (wpcom_getimagesize) to extract dimensions as a last resort if we weren't able to figure them out.
-	add_action( 'amp_extract_image_dimensions_batch', 'wpcom_amp_extract_image_dimensions_from_getimagesize', 99, 1 ); // Our last resort, so run late
+	add_action( 'amp_extract_image_dimensions_batch', 'wpcom_amp_extract_image_dimensions_from_getimagesize', 99, 1 ); // Our last resort, so run late.
 
 	// The wpcom override obviates this one, so take it out.
-	remove_filter( 'amp_extract_image_dimensions_batch', array( 'AMP_Image_Dimension_Extractor', 'extract_by_downloading_images' ), 999, 1 );
+	remove_filter( 'amp_extract_image_dimensions_batch', array( 'AMP_Image_Dimension_Extractor', 'extract_by_downloading_images' ), 999 );
 }
 
+/**
+ * Extract image dimensions from query string.
+ *
+ * @since 0.5
+ *
+ * @param array $dimensions Dimensions.
+ * @return array Dimensions.
+ */
 function wpcom_amp_extract_image_dimensions_from_querystring( $dimensions ) {
-	foreach ( $dimensions as $url => $value  ) {
+	foreach ( $dimensions as $url => $value ) {
 
 		if ( is_array( $value ) ) {
 			continue;
@@ -140,7 +198,7 @@ function wpcom_amp_extract_image_dimensions_from_querystring( $dimensions ) {
 
 		if ( false !== $w && false !== $h ) {
 			$dimensions[ $url ] = array(
-				'width' => $w,
+				'width'  => $w,
 				'height' => $h,
 			);
 		}
@@ -148,6 +206,14 @@ function wpcom_amp_extract_image_dimensions_from_querystring( $dimensions ) {
 	return $dimensions;
 }
 
+/**
+ * Extract image dimensions via wpcom/imagesize.
+ *
+ * @since 0.5
+ *
+ * @param array $dimensions Dimensions.
+ * @return array Dimensions.
+ */
 function wpcom_amp_extract_image_dimensions_from_getimagesize( $dimensions ) {
 	if ( ! function_exists( 'require_lib' ) ) {
 		return $dimensions;
@@ -161,7 +227,7 @@ function wpcom_amp_extract_image_dimensions_from_getimagesize( $dimensions ) {
 		$result = wpcom_getimagesize( $url );
 		if ( is_array( $result ) ) {
 			$dimensions[ $url ] = array(
-				'width' => $result[0],
+				'width'  => $result[0],
 				'height' => $result[1],
 			);
 		}