diff --git a/extensions/amp-ad/0.1/validator-amp-ad.protoascii b/extensions/amp-ad/0.1/validator-amp-ad.protoascii
new file mode 100644
index 000000000000..8503aa677b8c
--- /dev/null
+++ b/extensions/amp-ad/0.1/validator-amp-ad.protoascii
@@ -0,0 +1,106 @@
+#
+# Copyright 2016 The AMP HTML Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS-IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the license.
+
+# In the AMP Runtime, amp-ad and amp-embed are implemented in the samei
+# extension, so we include them both here.
+
+tags: {  # amp-ad
+  tag_name: "SCRIPT"
+  spec_name: "amp-ad extension .js script"
+  mandatory_parent: "HEAD"
+  attrs: {
+    name: "async"
+    mandatory: true
+    value: ""
+  }
+  attrs: {
+    name: "custom-element"
+    mandatory: true
+    value: "amp-ad"
+    dispatch_key: true
+  }
+  attrs: {
+    name: "src"
+    mandatory: true
+    value_regex: "https://cdn\\.ampproject\\.org/v0/amp-ad-(latest|0\\.1).js"
+  }
+  attrs: {
+    name: "type"
+    value: "text/javascript"
+  }
+  cdata: {
+    blacklisted_cdata_regex: {
+      regex: "."
+      error_message: "contents"
+    }
+  }
+  spec_url: "https://www.ampproject.org/docs/reference/extended/amp-ad.html"
+}
+tags: {  # <amp-ad>
+  tag_name: "AMP-AD"
+  # Typically we'd require the extension j/s, but for historical reasons
+  # many pages don't have it, so it ends up late loaded.
+  # TODO(gregable): Make the lack of the extension a deprecation warning.
+  # also_requires_tag: "amp-ad extension .js script"
+  disallowed_ancestor: "AMP-SIDEBAR"
+  attrs: { name: "alt" }
+  attrs: { name: "json" }
+  attrs: {
+    name: "src"
+    value_url: {
+      allowed_protocol: "https"
+      allow_relative: true  # Will be set to false at a future date.
+    }
+  }
+  attrs: { name: "type" mandatory: true }
+  attr_lists: "extended-amp-global"
+  spec_url: "https://www.ampproject.org/docs/reference/amp-ad.html"
+  amp_layout: {
+    supported_layouts: FILL
+    supported_layouts: FIXED
+    supported_layouts: FIXED_HEIGHT
+    supported_layouts: FLEX_ITEM
+    supported_layouts: NODISPLAY
+    supported_layouts: RESPONSIVE
+  }
+}
+tags: {  # <amp-embed>
+  tag_name: "AMP-EMBED"
+  # Typically we'd require the extension j/s, but for historical reasons
+  # many pages don't have it, so it ends up late loaded.
+  # TODO(gregable): Make the lack of the extension a deprecation warning.
+  # also_requires_tag: "amp-ad extension .js script"
+  disallowed_ancestor: "AMP-SIDEBAR"
+  attrs: { name: "alt" }
+  attrs: { name: "json" }
+  attrs: {
+    name: "src"
+    value_url: {
+      allowed_protocol: "https"
+      allow_relative: true  # Will be set to false at a future date.
+    }
+  }
+  attrs: { name: "type" mandatory: true }
+  attr_lists: "extended-amp-global"
+  spec_url: "https://www.ampproject.org/docs/reference/amp-embed.html"
+  amp_layout: {
+    supported_layouts: FILL
+    supported_layouts: FIXED
+    supported_layouts: FIXED_HEIGHT
+    supported_layouts: FLEX_ITEM
+    supported_layouts: NODISPLAY
+    supported_layouts: RESPONSIVE
+  }
+}
diff --git a/extensions/amp-form/0.1/validator-amp-form.protoascii b/extensions/amp-form/0.1/validator-amp-form.protoascii
new file mode 100644
index 000000000000..689d045c83fe
--- /dev/null
+++ b/extensions/amp-form/0.1/validator-amp-form.protoascii
@@ -0,0 +1,50 @@
+#
+# Copyright 2016 The AMP HTML Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS-IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the license.
+#
+tags: {  # amp-form
+  # Accepted form elements can be found in validator-main.protoascii
+  # under section "4.10 Forms"
+  tag_name: "SCRIPT"
+  spec_name: "amp-form extension .js script"
+  mandatory_parent: "HEAD"
+  attrs: {
+    name: "async"
+    mandatory: true
+    value: ""
+  }
+  attrs: {
+    name: "custom-element"
+    mandatory: true
+    value: "amp-form"
+    dispatch_key: true
+  }
+  attrs: {
+    name: "src"
+    mandatory: true
+    value_regex: "https://cdn\\.ampproject\\.org/v0/amp-form-(latest|0\\.1).js"
+  }
+  attrs: {
+    name: "type"
+    value: "text/javascript"
+  }
+  cdata: {
+    blacklisted_cdata_regex: {
+      regex: "."
+      error_message: "contents"
+    }
+  }
+  # TODO: update with ampproject.org url when available
+  spec_url: "https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md"
+}
diff --git a/extensions/amp-mustache/0.1/test/validator-amp-mustache.html b/extensions/amp-mustache/0.1/test/validator-amp-mustache.html
index 002ddf555adf..0eeda64db10e 100644
--- a/extensions/amp-mustache/0.1/test/validator-amp-mustache.html
+++ b/extensions/amp-mustache/0.1/test/validator-amp-mustache.html
@@ -46,6 +46,9 @@
   <p title="{{{notallowed}}}"></p>
   <p title="{{&notallowed}}"></p>
   <p title="{{>notallowed}}"></p>
+  <p data-title="{{{notallowed}}}"></p>
+  <p data-title="{{&notallowed}}"></p>
+  <p data-title="{{>notallowed}}"></p>
 
   <!-- now with some whitespace inside the mustache tags -->
   <{{ not-actually-parsed-as-an-html-tag-so-allowed }}>
diff --git a/extensions/amp-mustache/0.1/test/validator-amp-mustache.out b/extensions/amp-mustache/0.1/test/validator-amp-mustache.out
index 350871b433bf..8affa8725d18 100644
--- a/extensions/amp-mustache/0.1/test/validator-amp-mustache.out
+++ b/extensions/amp-mustache/0.1/test/validator-amp-mustache.out
@@ -14,25 +14,28 @@ amp-mustache/0.1/test/validator-amp-mustache.html:45:2 Mustache template syntax
 amp-mustache/0.1/test/validator-amp-mustache.html:46:2 The attribute 'title' in tag 'p' is set to '{{{notallowed}}}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
 amp-mustache/0.1/test/validator-amp-mustache.html:47:2 The attribute 'title' in tag 'p' is set to '{{&notallowed}}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
 amp-mustache/0.1/test/validator-amp-mustache.html:48:2 The attribute 'title' in tag 'p' is set to '{{>notallowed}}', which contains a Mustache template partial. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:53:2 Mustache template syntax in attribute name '{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:54:2 Mustache template syntax in attribute name '{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:55:2 Mustache template syntax in attribute name 'data-{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:56:2 Mustache template syntax in attribute name 'data-{{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:57:2 Mustache template syntax in attribute name 'data-{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:49:2 The attribute 'data-title' in tag 'p' is set to '{{{notallowed}}}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:50:2 The attribute 'data-title' in tag 'p' is set to '{{&notallowed}}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:51:2 The attribute 'data-title' in tag 'p' is set to '{{>notallowed}}', which contains a Mustache template partial. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:56:2 Mustache template syntax in attribute name '{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:57:2 Mustache template syntax in attribute name '{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
 amp-mustache/0.1/test/validator-amp-mustache.html:58:2 Mustache template syntax in attribute name 'data-{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:59:2 Mustache template syntax in attribute name 'data-{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:59:2 Mustache template syntax in attribute name 'data-{{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
 amp-mustache/0.1/test/validator-amp-mustache.html:60:2 Mustache template syntax in attribute name 'data-{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
 amp-mustache/0.1/test/validator-amp-mustache.html:61:2 Mustache template syntax in attribute name 'data-{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:62:2 Mustache template syntax in attribute name '{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:63:2 Mustache template syntax in attribute name '{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:64:2 The attribute 'title' in tag 'p' is set to '{{{ notallowed }}}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:65:2 The attribute 'title' in tag 'p' is set to '{{ &notallowed }}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:66:2 The attribute 'title' in tag 'p' is set to '{{ >notallowed }}', which contains a Mustache template partial. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:67:2 The attribute 'title' in tag 'p' is set to '{{& notallowed }}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:68:2 The attribute 'title' in tag 'p' is set to '{{> notallowed }}', which contains a Mustache template partial. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:69:2 The attribute 'title' in tag 'p' is set to '{{ & notallowed }}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:70:2 The attribute 'title' in tag 'p' is set to '{{ > notallowed }}', which contains a Mustache template partial. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:95:4 The tag 'template' may not appear as a descendant of tag 'template'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:107:0 The attribute 'autoplay' in tag 'amp-audio' is set to the invalid value '{{invalid}}'. (see https://www.ampproject.org/docs/reference/extended/amp-audio.html) [AMP_TAG_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:121:7 The tag 'amp-audio extension .js script' is missing or incorrect, but required by 'amp-audio'. (see https://www.ampproject.org/docs/reference/extended/amp-audio.html) [AMP_TAG_PROBLEM]
-amp-mustache/0.1/test/validator-amp-mustache.html:121:7 The tag 'amp-mustache extension .js script' is missing or incorrect, but required by 'template'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_TAG_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:62:2 Mustache template syntax in attribute name 'data-{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:63:2 Mustache template syntax in attribute name 'data-{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:64:2 Mustache template syntax in attribute name 'data-{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:65:2 Mustache template syntax in attribute name '{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:66:2 Mustache template syntax in attribute name '{{' in tag 'p'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:67:2 The attribute 'title' in tag 'p' is set to '{{{ notallowed }}}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:68:2 The attribute 'title' in tag 'p' is set to '{{ &notallowed }}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:69:2 The attribute 'title' in tag 'p' is set to '{{ >notallowed }}', which contains a Mustache template partial. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:70:2 The attribute 'title' in tag 'p' is set to '{{& notallowed }}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:71:2 The attribute 'title' in tag 'p' is set to '{{> notallowed }}', which contains a Mustache template partial. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:72:2 The attribute 'title' in tag 'p' is set to '{{ & notallowed }}', which contains unescaped Mustache template syntax. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:73:2 The attribute 'title' in tag 'p' is set to '{{ > notallowed }}', which contains a Mustache template partial. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:98:4 The tag 'template' may not appear as a descendant of tag 'template'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_HTML_TEMPLATE_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:110:0 The attribute 'autoplay' in tag 'amp-audio' is set to the invalid value '{{invalid}}'. (see https://www.ampproject.org/docs/reference/extended/amp-audio.html) [AMP_TAG_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:124:7 The tag 'amp-audio extension .js script' is missing or incorrect, but required by 'amp-audio'. (see https://www.ampproject.org/docs/reference/extended/amp-audio.html) [AMP_TAG_PROBLEM]
+amp-mustache/0.1/test/validator-amp-mustache.html:124:7 The tag 'amp-mustache extension .js script' is missing or incorrect, but required by 'template'. (see https://www.ampproject.org/docs/reference/extended/amp-mustache.html) [AMP_TAG_PROBLEM]
diff --git a/validator/index.js b/validator/index.js
index b5183d0cddd1..733b7c50dfa5 100755
--- a/validator/index.js
+++ b/validator/index.js
@@ -30,6 +30,12 @@ var url = require('url');
 var util = require('util');
 var vm = require('vm');
 
+/**
+ * Determines if str begins with prefix.
+ * @param {!string} str
+ * @param {!string} prefix
+ * @returns {!boolean}
+ */
 function hasPrefix(str, prefix) {
   return str.indexOf(prefix) == 0;
 }
@@ -263,7 +269,7 @@ Validator.prototype.validateString =
     result.errors.push(error);
   }
   return result;
-}
+};
 
 /**
  * A global static map used by the getInstance function to avoid loading
@@ -320,7 +326,7 @@ function logValidationResult(filename, validationResult, color) {
       msg += (error.severity === 'ERROR' ? colors.red : colors.magenta)(
           error.message);
     } else {
-      msg += error.message
+      msg += error.message;
     }
     if (error.specUrl) {
       msg += ' (see ' + error.specUrl + ')';
@@ -393,7 +399,7 @@ function main() {
                 }
               }
               if (program.format === 'json') {
-                console.log(JSON.stringify(jsonOut))
+                console.log(JSON.stringify(jsonOut));
               }
             })
             .catch(function(error) {
diff --git a/validator/testdata/feature_tests/forms.html b/validator/testdata/feature_tests/forms.html
new file mode 100644
index 000000000000..8cf887a20233
--- /dev/null
+++ b/validator/testdata/feature_tests/forms.html
@@ -0,0 +1,75 @@
+<!--
+  Copyright 2016 The AMP HTML Authors. All Rights Reserved.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+      http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS-IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the license.
+-->
+<!--
+  Test Description:
+  This tests looks at specific errors related to forms.
+-->
+<!doctype html>
+<html ⚡>
+<head>
+  <meta charset="utf-8">
+  <link rel="canonical" href="./regular-html-version.html" />
+  <meta name="viewport" content="width=device-width,minimum-scale=1">
+  <style amp-boilerplate>body{-webkit-animation:-amp-start 8s steps(1,end) 0s 1 normal both;-moz-animation:-amp-start 8s steps(1,end) 0s 1 normal both;-ms-animation:-amp-start 8s steps(1,end) 0s 1 normal both;animation:-amp-start 8s steps(1,end) 0s 1 normal both}@-webkit-keyframes -amp-start{from{visibility:hidden}to{visibility:visible}}@-moz-keyframes -amp-start{from{visibility:hidden}to{visibility:visible}}@-ms-keyframes -amp-start{from{visibility:hidden}to{visibility:visible}}@-o-keyframes -amp-start{from{visibility:hidden}to{visibility:visible}}@keyframes -amp-start{from{visibility:hidden}to{visibility:visible}}</style><noscript><style amp-boilerplate>body{-webkit-animation:none;-moz-animation:none;-ms-animation:none;animation:none}</style></noscript>
+  <script async src="https://cdn.ampproject.org/v0.js"></script>
+  <script async custom-element="amp-form" src="https://cdn.ampproject.org/v0/amp-form-0.1.js"></script>
+</head>
+<body>
+  <!-- Valid form -->
+  <form method="post" action="https://example.com/subscribe" target="_blank">
+    <fieldset>
+      <label>
+        <span>Your name</span>
+        <input type="text" name="name" required>
+      </label>
+      <label>
+        <span>Your email</span>
+        <input type="email" name="email" required>
+      </label>
+      <input type="submit" value="Subscribe">
+    </fieldset>
+  </form>
+  <!-- Invalid form action must not be a relative url -->
+  <form method="post" action="/subscribe" target="_blank">
+    <input type="submit" value="Subscribe">
+  </form>
+  <!-- Invalid: form action must be https. -->
+  <form method="post" action="http://example.com/subscribe" target="_blank">
+    <input type="submit" value="Subscribe">
+  </form>
+  <!-- Invalid: form action must be a non-cdn link. -->
+  <form method="post" action="https://cdn.ampproject.org/subscribe" target="_blank">
+    <input type="submit" value="Subscribe">
+  </form>
+  <!-- Invalid: form target must be _blank or _top -->
+  <form method="post" action="https://example/subscribe" target="_new">
+    <input type="submit" value="Subscribe">
+  </form>
+  <!-- Invalid: input, select, option and textarea must be children of form. -->
+  <input type="text" name="name">
+  <select name="language">
+    <option value="1">English</option>
+  </select>
+  <textarea name="comment"></textarea>
+  <!-- Invalid: input can not be type="button|file|image|password". -->
+  <form method="post" action="https://example.com/subscribe" target="_blank">
+    <input type="button" name="button">
+    <input type="file" name="file">
+    <input type="image" name="image">
+    <input type="password" name="password">
+  </form>
+</body>
+</html>
diff --git a/validator/testdata/feature_tests/forms.out b/validator/testdata/feature_tests/forms.out
new file mode 100644
index 000000000000..4b780f907da5
--- /dev/null
+++ b/validator/testdata/feature_tests/forms.out
@@ -0,0 +1,13 @@
+FAIL
+feature_tests/forms.html:46:2 The relative URL '/subscribe' for attribute 'action' in tag 'form' is disallowed. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
+feature_tests/forms.html:50:2 Invalid URL protocol 'http:' for attribute 'action' in tag 'form'. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
+feature_tests/forms.html:54:2 The domain 'cdn.ampproject.org' for attribute 'action' in tag 'form' is disallowed. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
+feature_tests/forms.html:58:2 The attribute 'target' in tag 'form' is set to the invalid value '_new'. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
+feature_tests/forms.html:62:2 The tag 'input' may only appear as a descendant of tag 'form'. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
+feature_tests/forms.html:63:2 The tag 'select' may only appear as a descendant of tag 'form'. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
+feature_tests/forms.html:64:4 The tag 'option' may only appear as a descendant of tag 'form'. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
+feature_tests/forms.html:66:2 The tag 'textarea' may only appear as a descendant of tag 'form'. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
+feature_tests/forms.html:69:4 The attribute 'type' in tag 'input' is set to the invalid value 'button'. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
+feature_tests/forms.html:70:4 The attribute 'type' in tag 'input' is set to the invalid value 'file'. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
+feature_tests/forms.html:71:4 The attribute 'type' in tag 'input' is set to the invalid value 'image'. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
+feature_tests/forms.html:72:4 The attribute 'type' in tag 'input' is set to the invalid value 'password'. (see https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md) [DISALLOWED_HTML]
diff --git a/validator/testdata/feature_tests/urls.html b/validator/testdata/feature_tests/urls.html
index bae63c27120d..d57c347d42fd 100644
--- a/validator/testdata/feature_tests/urls.html
+++ b/validator/testdata/feature_tests/urls.html
@@ -42,7 +42,6 @@
   <a href="vbscript:bar">Invalid protocol</a>
   <a href="data:baz">Invalid protocol</a>
   <a href="ftp://google.com/">Valid protocol</a>
-  <a href="http://site:80808/%AFpage">Malformed URL</a>
   <!-- invalid (javascript is not an allowed protocol: singluar src element) -->
   <amp-img srcset="javascript:alert(1)" layout="fill"></amp-img>
   <!-- invalid (javascript is not an allwoed protocol: second src element) -->
@@ -57,8 +56,6 @@
   <amp-img srcset="javascript:alert('boo') 1x, foo 2x" layout="fill"></amp-img>
   <!-- invalid (javascript is not an allowed protocol: case insensitive) -->
   <amp-img srcset="image-1x.png 1x, JavaScript:baz 2x" layout="fill"></amp-img>
-  <!-- invalid (not a valid URL) -->
-  <amp-img srcset="http://site:80808/%AFimg 1x, img 2x" layout="fill"></amp-img>
   <!-- invalid (empty) -->
   <amp-img srcset="" layout="fill"></amp-img>
   <!-- invalid (duplicate pixel density) -->
diff --git a/validator/testdata/feature_tests/urls.out b/validator/testdata/feature_tests/urls.out
index aa6e4e78cedf..d528a36ea01b 100644
--- a/validator/testdata/feature_tests/urls.out
+++ b/validator/testdata/feature_tests/urls.out
@@ -5,25 +5,23 @@ feature_tests/urls.html:40:2 Invalid URL protocol 'javascript:' for attribute 'h
 feature_tests/urls.html:41:2 Invalid URL protocol 'javascript:' for attribute 'href' in tag 'a'. [DISALLOWED_HTML]
 feature_tests/urls.html:42:2 Invalid URL protocol 'vbscript:' for attribute 'href' in tag 'a'. [DISALLOWED_HTML]
 feature_tests/urls.html:43:2 Invalid URL protocol 'data:' for attribute 'href' in tag 'a'. [DISALLOWED_HTML]
-feature_tests/urls.html:45:2 Malformed URL 'http://site:80808/%AFpage' for attribute 'href' in tag 'a'. [DISALLOWED_HTML]
-feature_tests/urls.html:47:2 Invalid URL protocol 'javascript:' for attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:49:2 Multiple image candidates with the same width or pixel density found in attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [DISALLOWED_HTML]
-feature_tests/urls.html:57:2 Invalid URL protocol 'javascript:' for attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:59:2 Invalid URL protocol 'javascript:' for attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:61:2 Malformed URL 'http://site:80808/%AFimg' for attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:63:2 Missing URL for attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:65:2 Multiple image candidates with the same width or pixel density found in attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [DISALLOWED_HTML]
-feature_tests/urls.html:67:2 The attribute 'srcset' in tag 'amp-img' is set to the invalid value 'image 1x.png 1x, image 2x.png 2x'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:72:2 Missing URL for attribute 'src' in tag 'amp-ad'. (see https://www.ampproject.org/docs/reference/amp-ad.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:73:2 Missing URL for attribute 'src' in tag 'amp-anim'. (see https://www.ampproject.org/docs/reference/extended/amp-anim.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:74:2 Missing URL for attribute 'src' in tag 'amp-audio'. (see https://www.ampproject.org/docs/reference/extended/amp-audio.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:75:2 Missing URL for attribute 'src' in tag 'amp-iframe'. (see https://www.ampproject.org/docs/reference/extended/amp-iframe.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:76:2 Missing URL for attribute 'src' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:77:2 Missing URL for attribute 'src' in tag 'amp-pixel'. (see https://www.ampproject.org/docs/reference/amp-pixel.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:78:2 Missing URL for attribute 'src' in tag 'amp-video'. (see https://www.ampproject.org/docs/reference/amp-video.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:80:2 Invalid URL protocol 'http:' for attribute 'src' in tag 'amp-ad'. (see https://www.ampproject.org/docs/reference/amp-ad.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:81:2 Invalid URL protocol 'http:' for attribute 'src' in tag 'amp-iframe'. (see https://www.ampproject.org/docs/reference/extended/amp-iframe.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:82:2 Invalid URL protocol 'http:' for attribute 'src' in tag 'amp-pixel'. (see https://www.ampproject.org/docs/reference/amp-pixel.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:83:2 Invalid URL protocol 'http:' for attribute 'src' in tag 'amp-video'. (see https://www.ampproject.org/docs/reference/amp-video.html) [AMP_TAG_PROBLEM]
-feature_tests/urls.html:84:2 Invalid URL protocol 'j a v a s c r i p t :' for attribute 'href' in tag 'a'. [DISALLOWED_HTML]
-feature_tests/urls.html:86:7 The mandatory tag 'link rel=canonical' is missing or incorrect. (see https://www.ampproject.org/docs/reference/spec.html#required-markup) [MANDATORY_AMP_TAG_MISSING_OR_INCORRECT]
+feature_tests/urls.html:46:2 Invalid URL protocol 'javascript:' for attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:48:2 Multiple image candidates with the same width or pixel density found in attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [DISALLOWED_HTML]
+feature_tests/urls.html:56:2 Invalid URL protocol 'javascript:' for attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:58:2 Invalid URL protocol 'javascript:' for attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:60:2 Missing URL for attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:62:2 Multiple image candidates with the same width or pixel density found in attribute 'srcset' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [DISALLOWED_HTML]
+feature_tests/urls.html:64:2 The attribute 'srcset' in tag 'amp-img' is set to the invalid value 'image 1x.png 1x, image 2x.png 2x'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:69:2 Missing URL for attribute 'src' in tag 'amp-ad'. (see https://www.ampproject.org/docs/reference/amp-ad.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:70:2 Missing URL for attribute 'src' in tag 'amp-anim'. (see https://www.ampproject.org/docs/reference/extended/amp-anim.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:71:2 Missing URL for attribute 'src' in tag 'amp-audio'. (see https://www.ampproject.org/docs/reference/extended/amp-audio.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:72:2 Missing URL for attribute 'src' in tag 'amp-iframe'. (see https://www.ampproject.org/docs/reference/extended/amp-iframe.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:73:2 Missing URL for attribute 'src' in tag 'amp-img'. (see https://www.ampproject.org/docs/reference/amp-img.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:74:2 Missing URL for attribute 'src' in tag 'amp-pixel'. (see https://www.ampproject.org/docs/reference/amp-pixel.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:75:2 Missing URL for attribute 'src' in tag 'amp-video'. (see https://www.ampproject.org/docs/reference/amp-video.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:77:2 Invalid URL protocol 'http:' for attribute 'src' in tag 'amp-ad'. (see https://www.ampproject.org/docs/reference/amp-ad.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:78:2 Invalid URL protocol 'http:' for attribute 'src' in tag 'amp-iframe'. (see https://www.ampproject.org/docs/reference/extended/amp-iframe.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:79:2 Invalid URL protocol 'http:' for attribute 'src' in tag 'amp-pixel'. (see https://www.ampproject.org/docs/reference/amp-pixel.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:80:2 Invalid URL protocol 'http:' for attribute 'src' in tag 'amp-video'. (see https://www.ampproject.org/docs/reference/amp-video.html) [AMP_TAG_PROBLEM]
+feature_tests/urls.html:81:2 Invalid URL protocol 'j a v a s c r i p t :' for attribute 'href' in tag 'a'. [DISALLOWED_HTML]
+feature_tests/urls.html:83:7 The mandatory tag 'link rel=canonical' is missing or incorrect. (see https://www.ampproject.org/docs/reference/spec.html#required-markup) [MANDATORY_AMP_TAG_MISSING_OR_INCORRECT]
diff --git a/validator/validator-full.js b/validator/validator-full.js
index 1acf7d3cfd98..7f69a4c42e2f 100644
--- a/validator/validator-full.js
+++ b/validator/validator-full.js
@@ -145,6 +145,10 @@ amp.validator.ValidationResult.prototype.outputToTerminal = function(
       terminal.warn(errorLine(url, error));
     }
   }
+  if (errorCategoryFilter === null && errors.length !== 0) {
+    terminal.info('See also https://validator.ampproject.org/#url=' +
+        encodeURIComponent(goog.uri.utils.removeFragment(url)));
+  }
 };
 
 /**
@@ -337,6 +341,8 @@ amp.validator.categorizeError = function(error) {
            amp.validator.ValidationError.Code.CSS_SYNTAX_INVALID_URL ||
        error.code ===
            amp.validator.ValidationError.Code.CSS_SYNTAX_INVALID_URL_PROTOCOL ||
+       error.code ===
+           amp.validator.ValidationError.Code.CSS_SYNTAX_DISALLOWED_DOMAIN ||
        error.code ===
            amp.validator.ValidationError.Code
                .CSS_SYNTAX_DISALLOWED_RELATIVE_URL) &&
@@ -519,6 +525,7 @@ amp.validator.categorizeError = function(error) {
   if (error.code == amp.validator.ValidationError.Code.MISSING_URL ||
       error.code == amp.validator.ValidationError.Code.INVALID_URL ||
       error.code == amp.validator.ValidationError.Code.INVALID_URL_PROTOCOL ||
+      error.code == amp.validator.ValidationError.Code.DISALLOWED_DOMAIN ||
       error.code ==
           amp.validator.ValidationError.Code.DISALLOWED_RELATIVE_URL) {
     if (goog.string./*OK*/ startsWith(error.params[1], 'amp-')) {
diff --git a/validator/validator-main.protoascii b/validator/validator-main.protoascii
index e84532111218..50da911e73ec 100644
--- a/validator/validator-main.protoascii
+++ b/validator/validator-main.protoascii
@@ -20,12 +20,12 @@
 # in production from crashing. This id is not relevant to validator.js
 # because thus far, engine (validator.js) and spec file
 # (validator-main.protoascii) are always released together.
-min_validator_revision_required: 135
+min_validator_revision_required: 143
 # The spec file revision allows the validator engine to distinguish
 # newer versions of the spec file. This is currently a Google internal
 # mechanism, validator.js does not use this facility. However, any
 # change to this file (validator-main.js) requires updating this revision id.
-spec_file_revision: 231
+spec_file_revision: 235
 
 # Validator extensions.
 # =====================
@@ -716,6 +716,7 @@ attr_lists: {
       allowed_protocol: "fb-messenger"
       allowed_protocol: "sms"
       allowed_protocol: "tel"
+      allowed_protocol: "threema"
       allowed_protocol: "viber"
       allowed_protocol: "whatsapp"
     }
@@ -800,6 +801,7 @@ tags: {
       allowed_protocol: "fb-messenger"
       allowed_protocol: "sms"
       allowed_protocol: "tel"
+      allowed_protocol: "threema"
       allowed_protocol: "viber"
       allowed_protocol: "whatsapp"
       allow_relative: true
@@ -1902,7 +1904,94 @@ tags: {
 }
 
 # 4.10 Forms
-# Not allowed, except for button.
+# Form elements are allowed only when amp-form extension script is included
+# with the exception of the button element which is always allowed.
+# 4.10.3 The form element
+tags {
+  tag_name: "FORM"
+  also_requires_tag: "amp-form extension .js script"
+  attrs: { name: "accept" }
+  attrs: { name: "accept-charset" }
+  attrs: {
+    name: "action"
+    mandatory: true
+    value_url: {
+      allow_relative: false
+      allowed_protocol: "https"
+      disallowed_domain: "cdn.ampproject.org"
+    }
+  }
+  attrs: { name: "action-xhr" }
+  attrs: { name: "autocomplete" }
+  attrs: { name: "enctype" }
+  attrs: { name: "method" }
+  attrs: { name: "name" }
+  attrs: { name: "novalidate" }
+  attrs: {
+    name: "target"
+    mandatory: true
+    value_regex_casei: "(_blank|_top)"
+  }
+  # TODO: update with ampproject.org url when available
+  spec_url: "https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md"
+}
+# 4.10.4 The label element
+tags: {
+  tag_name: "LABEL"
+  mandatory_ancestor: "FORM"
+  also_requires_tag: "amp-form extension .js script"
+  attrs: { name: "for" }
+  attrs: { name: "form" }
+  # TODO: update with ampproject.org url when available
+  spec_url: "https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md"
+}
+# 4.10.5 The input element
+tags: {
+  tag_name: "INPUT"
+  mandatory_ancestor: "FORM"
+  also_requires_tag: "amp-form extension .js script"
+  attrs: { name: "accept" }
+  attrs: { name: "accesskey" }
+  attrs: { name: "autocomplete" }
+  attrs: { name: "autofocus" }
+  attrs: { name: "checked" }
+  attrs: { name: "disabled" }
+  attrs: { name: "form" }
+  attrs: { name: "formmethod" }
+  attrs: { name: "formnovalidate" }
+  attrs: { name: "height" }
+  attrs: { name: "inputmode" }
+  attrs: { name: "list" }
+  attrs: { name: "max" }
+  attrs: { name: "maxlength" }
+  attrs: { name: "min" }
+  attrs: { name: "minlength" }
+  attrs: { name: "multiple" }
+  attrs: { name: "name" }
+  attrs: { name: "pattern" }
+  attrs: { name: "placeholder" }
+  attrs: { name: "readonly" }
+  attrs: { name: "required" }
+  attrs: { name: "selectiondirection" }
+  attrs: { name: "size" }
+  attrs: { name: "spellcheck" }
+  attrs: { name: "step" }
+  attrs: { name: "tabindex" }
+  attrs: {
+    name: "type"
+    blacklisted_value_regex: "(^|\\s)("  # Values are space separated.
+        "button|"
+        "file|"
+        "image|"
+        "password|"
+        ")(\\s|$)"
+  }
+  attrs: { name: "value" }
+  attrs: { name: "width" }
+  # TODO: update with ampproject.org url when available
+  spec_url: "https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md"
+}
+# 4.10.6 The button element
 tags: {
   tag_name: "BUTTON"
   attrs: {
@@ -1921,6 +2010,69 @@ tags: {
   attrs: { name: "type" }
   attrs: { name: "value" }
 }
+# 4.10.7 The select element
+tags: {
+  tag_name: "SELECT"
+  mandatory_ancestor: "FORM"
+  also_requires_tag: "amp-form extension .js script"
+  attrs: { name: "autofocus" }
+  attrs: { name: "disabled" }
+  attrs: { name: "form" }
+  attrs: { name: "multiple" }
+  attrs: { name: "name" }
+  attrs: { name: "required" }
+  attrs: { name: "size" }
+  # TODO: update with ampproject.org url when available
+  spec_url: "https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md"
+}
+# 4.10.10 The option element
+tags: {
+  tag_name: "OPTION"
+  mandatory_ancestor: "FORM"
+  also_requires_tag: "amp-form extension .js script"
+  attrs: { name: "disabled" }
+  attrs: { name: "label" }
+  attrs: { name: "selected" }
+  attrs: { name: "value" }
+  # TODO: update with ampproject.org url when available
+  spec_url: "https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md"
+}
+# 4.10.11 The textarea element
+tags: {
+  tag_name: "TEXTAREA"
+  mandatory_ancestor: "FORM"
+  also_requires_tag: "amp-form extension .js script"
+  attrs: { name: "autocomplete" }
+  attrs: { name: "autofocus" }
+  attrs: { name: "cols" }
+  attrs: { name: "disabled" }
+  attrs: { name: "form" }
+  attrs: { name: "maxlength" }
+  attrs: { name: "minlength" }
+  attrs: { name: "name" }
+  attrs: { name: "placeholder" }
+  attrs: { name: "readonly" }
+  attrs: { name: "required" }
+  attrs: { name: "rows" }
+  attrs: { name: "selectiondirection" }
+  attrs: { name: "selectionend" }
+  attrs: { name: "selectionstart" }
+  attrs: { name: "spellcheck" }
+  attrs: { name: "wrap"}
+  # TODO: update with ampproject.org url when available
+  spec_url: "https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md"
+}
+# 4.10.16 The fieldset element
+tags: {
+  tag_name: "FIELDSET"
+  mandatory_ancestor: "FORM"
+  also_requires_tag: "amp-form extension .js script"
+  attrs: { name: "disabled" }
+  attrs: { name: "form" }
+  attrs: { name: "name" }
+  # TODO: update with ampproject.org url when available
+  spec_url: "https://github.com/ampproject/amphtml/blob/master/extensions/amp-form/amp-form.md"
+}
 
 # 4.11 Scripting
 # 4.11.1 The script element
@@ -2066,58 +2218,6 @@ attr_lists: {
   attrs: { name: "media" }
   attrs: { name: "noloading" value: "" }
 }
-# In the AMP Runtime, amp-ad and amp-embed are implemented in the same way,
-# so if you're changing amp-ad consider changing amp-embed as well.
-tags: {  # <amp-ad>
-  tag_name: "AMP-AD"
-  disallowed_ancestor: "AMP-SIDEBAR"
-  attrs: { name: "alt" }
-  attrs: { name: "json" }
-  attrs: {
-    name: "src"
-    value_url: {
-      allowed_protocol: "https"
-      allow_relative: true  # Will be set to false at a future date.
-    }
-  }
-  attrs: { name: "type" mandatory: true }
-  attr_lists: "extended-amp-global"
-  spec_url: "https://www.ampproject.org/docs/reference/amp-ad.html"
-  amp_layout: {
-    supported_layouts: FILL
-    supported_layouts: FIXED
-    supported_layouts: FIXED_HEIGHT
-    supported_layouts: FLEX_ITEM
-    supported_layouts: NODISPLAY
-    supported_layouts: RESPONSIVE
-  }
-}
-# In the AMP Runtime, amp-ad and amp-embed are implemented in the same way,
-# so if you're changing amp-embed consider changing amp-ad as well.
-tags: {  # <amp-embed>
-  tag_name: "AMP-EMBED"
-  disallowed_ancestor: "AMP-SIDEBAR"
-  attrs: { name: "alt" }
-  attrs: { name: "json" }
-  attrs: {
-    name: "src"
-    value_url: {
-      allowed_protocol: "https"
-      allow_relative: true  # Will be set to false at a future date.
-    }
-  }
-  attrs: { name: "type" mandatory: true }
-  attr_lists: "extended-amp-global"
-  spec_url: "https://www.ampproject.org/docs/reference/amp-embed.html"
-  amp_layout: {
-    supported_layouts: FILL
-    supported_layouts: FIXED
-    supported_layouts: FIXED_HEIGHT
-    supported_layouts: FLEX_ITEM
-    supported_layouts: NODISPLAY
-    supported_layouts: RESPONSIVE
-  }
-}
 tags: {  # <amp-img>
   tag_name: "AMP-IMG"
   # <amp-img> is whitelisted for <amp-sidebar>, otherwise:
@@ -2392,6 +2492,10 @@ error_formats {
   code: INVALID_URL_PROTOCOL
   format: "Invalid URL protocol '%3:' for attribute '%1' in tag '%2'."
 }
+error_formats {
+  code: DISALLOWED_DOMAIN
+  format: "The domain '%3' for attribute '%1' in tag '%2' is disallowed."
+}
 error_formats {
   code: DISALLOWED_RELATIVE_URL
   format: "The relative URL '%3' for attribute '%1' in tag '%2' is disallowed."
@@ -2548,6 +2652,10 @@ error_formats {
   code: CSS_SYNTAX_INVALID_URL_PROTOCOL
   format: "CSS syntax error in tag '%1' - invalid url protocol '%2:'."
 }
+error_formats {
+  code: CSS_SYNTAX_DISALLOWED_DOMAIN
+  format: "CSS syntax error in tag '%1' - invalid domain '%2'."
+}
 error_formats {
   code: CSS_SYNTAX_DISALLOWED_RELATIVE_URL
   format: "CSS syntax error in tag '%1' - disallowed relative url '%2'."
diff --git a/validator/validator.js b/validator/validator.js
index a674c5704f28..ca3cee5be900 100644
--- a/validator/validator.js
+++ b/validator/validator.js
@@ -31,10 +31,10 @@ goog.require('amp.validator.ValidationError.Severity');
 goog.require('amp.validator.ValidationResult');
 goog.require('amp.validator.ValidationResult.Status');
 goog.require('amp.validator.ValidatorRules');
-goog.require('goog.Uri');
 goog.require('goog.array');
 goog.require('goog.asserts');
 goog.require('goog.string');
+goog.require('goog.uri.utils');
 goog.require('parse_css.BlockType');
 goog.require('parse_css.ParsedCssUrl');
 goog.require('parse_css.RuleVisitor');
@@ -935,7 +935,7 @@ class ParsedUrlSpec {
     this.spec_ = spec;
 
     /**
-     * @type {!Object<string, ?>}
+     * @type {!Object<string, int>}
      * @private
      */
     this.allowedProtocols_ = {};
@@ -944,6 +944,17 @@ class ParsedUrlSpec {
         this.allowedProtocols_[protocol] = 0;
       }
     }
+
+    /**
+     * @type {!Object<string, int>}
+     * @private
+     */
+    this.disallowedDomains_ = {};
+    if (this.spec_ !== null) {
+      for (const domain of this.spec_.disallowedDomain) {
+        this.disallowedDomains_[domain] = 0;
+      }
+    }
   }
 
   /**
@@ -990,10 +1001,8 @@ class ParsedUrlSpec {
       }
       return;
     }
-    let uri;
-    try {
-      uri = goog.Uri.parse(url);
-    } catch (ex) {
+    const urlComponents = goog.uri.utils.split(url);
+    if (urlComponents === null) {
       if (amp.validator.GENERATE_DETAILED_ERRORS) {
         adapter.invalidUrl(context, url, tagSpec, result);
       } else {
@@ -1001,17 +1010,18 @@ class ParsedUrlSpec {
       }
       return;
     }
-    if (uri.hasScheme() &&
-        !this.allowedProtocols_.hasOwnProperty(uri.getScheme().toLowerCase())) {
+    const scheme = urlComponents[goog.uri.utils.ComponentIndex.SCHEME];
+    if (scheme &&
+        !this.allowedProtocols_.hasOwnProperty(scheme.toLowerCase())) {
       if (amp.validator.GENERATE_DETAILED_ERRORS) {
         adapter.invalidUrlProtocol(
-            context, uri.getScheme().toLowerCase(), tagSpec, result);
+            context, scheme.toLowerCase(), tagSpec, result);
       } else {
         result.status = amp.validator.ValidationResult.Status.FAIL;
       }
       return;
     }
-    if (!this.spec_.allowRelative && !uri.hasScheme()) {
+    if (!this.spec_.allowRelative && (scheme === undefined)) {
       if (amp.validator.GENERATE_DETAILED_ERRORS) {
         adapter.disallowedRelativeUrl(context, url, tagSpec, result);
       } else {
@@ -1019,6 +1029,17 @@ class ParsedUrlSpec {
       }
       return;
     }
+    const domain = urlComponents[goog.uri.utils.ComponentIndex.DOMAIN];
+    if (domain &&
+        this.disallowedDomains_.hasOwnProperty(domain.toLowerCase())) {
+      if (amp.validator.GENERATE_DETAILED_ERRORS) {
+        adapter.disallowedDomain(
+            context, domain.toLowerCase(), tagSpec, result);
+      } else {
+        result.status = amp.validator.ValidationResult.Status.FAIL;
+      }
+      return;
+    }
   }
 }
 
@@ -1073,6 +1094,21 @@ ParsedUrlSpec.AttrErrorAdapter_ = class {
         tagSpec.specUrl, result);
   }
 
+  /**
+   * @param {!Context} context
+   * @param {string} domain
+   * @param {!amp.validator.TagSpec} tagSpec
+   * @param {!amp.validator.ValidationResult} result
+   */
+  disallowedDomain(context, domain, tagSpec, result) {
+    context.addError(
+        amp.validator.ValidationError.Severity.ERROR,
+        amp.validator.ValidationError.Code.DISALLOWED_DOMAIN,
+        context.getDocLocator(),
+        /* params */[this.attrName_, getTagSpecName(tagSpec), domain],
+        tagSpec.specUrl, result);
+  }
+
   /**
    * @param {!Context} context
    * @param {string} url
@@ -1147,6 +1183,20 @@ ParsedUrlSpec.StylesheetErrorAdapter_ = class {
         result);
   }
 
+  /**
+   * @param {!Context} context
+   * @param {string} domain
+   * @param {!amp.validator.TagSpec} tagSpec
+   * @param {!amp.validator.ValidationResult} result
+   */
+  disallowedDomain(context, domain, tagSpec, result) {
+    context.addError(
+        amp.validator.ValidationError.Severity.ERROR,
+        amp.validator.ValidationError.Code.CSS_SYNTAX_DISALLOWED_DOMAIN,
+        this.lineCol_,
+        /* params */[getTagSpecName(tagSpec), domain], tagSpec.specUrl, result);
+  }
+
   /**
    * @param {!Context} context
    * @param {string} url
@@ -1890,7 +1940,7 @@ function makeDispatchKey(attrName, attrValue, mandatoryParent) {
  */
 class ParsedTagSpec {
   /**
-   * @param {string} templateSpecUrl
+   * @param {?string} templateSpecUrl
    * @param {!ParsedAttrLists} parsedAttrLists
    * @param {!Object<string, number>} tagspecIdsByTagSpecName
    * @param {boolean} shouldRecordTagspecValidated
@@ -1935,7 +1985,7 @@ class ParsedTagSpec {
      */
     this.mandatoryOneofs_ = [];
     /**
-     * @type {string}
+     * @type {?string}
      * @private
      */
     this.templateSpecUrl_ = templateSpecUrl;
@@ -2427,6 +2477,13 @@ class ParsedTagSpec {
         if (result.status === amp.validator.ValidationResult.Status.FAIL) {
           return;
         }
+        if (hasTemplateAncestor) {
+          this.validateAttrValueBelowTemplateTag(
+              context, attrName, attrValue, result);
+          if (result.status === amp.validator.ValidationResult.Status.FAIL) {
+            return;
+          }
+        }
         continue;
       }
       if (hasTemplateAncestor) {
@@ -2830,50 +2887,54 @@ function specificity(code) {
       return 35;
     case amp.validator.ValidationError.Code.MISSING_URL:
       return 36;
-    case amp.validator.ValidationError.Code.INVALID_URL_PROTOCOL:
+    case amp.validator.ValidationError.Code.DISALLOWED_DOMAIN:
       return 37;
-    case amp.validator.ValidationError.Code.INVALID_URL:
+    case amp.validator.ValidationError.Code.INVALID_URL_PROTOCOL:
       return 38;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_STRAY_TRAILING_BACKSLASH:
+    case amp.validator.ValidationError.Code.INVALID_URL:
       return 39;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_UNTERMINATED_COMMENT:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_STRAY_TRAILING_BACKSLASH:
       return 40;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_UNTERMINATED_STRING:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_UNTERMINATED_COMMENT:
       return 41;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_BAD_URL:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_UNTERMINATED_STRING:
       return 42;
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_BAD_URL:
+      return 43;
     case amp.validator.ValidationError.Code
         .CSS_SYNTAX_EOF_IN_PRELUDE_OF_QUALIFIED_RULE:
-      return 43;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_INVALID_DECLARATION:
       return 44;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_INCOMPLETE_DECLARATION:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_INVALID_DECLARATION:
       return 45;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_ERROR_IN_PSEUDO_SELECTOR:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_INCOMPLETE_DECLARATION:
       return 46;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_MISSING_SELECTOR:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_ERROR_IN_PSEUDO_SELECTOR:
       return 47;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_NOT_A_SELECTOR_START:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_MISSING_SELECTOR:
       return 48;
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_NOT_A_SELECTOR_START:
+      return 49;
     case amp.validator.ValidationError.Code
         .CSS_SYNTAX_UNPARSED_INPUT_REMAINS_IN_SELECTOR:
-      return 49;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_MISSING_URL:
       return 50;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_INVALID_URL:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_MISSING_URL:
       return 51;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_INVALID_URL_PROTOCOL:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_DISALLOWED_DOMAIN:
       return 52;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_DISALLOWED_RELATIVE_URL:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_INVALID_URL:
       return 53;
-    case amp.validator.ValidationError.Code.INCORRECT_NUM_CHILD_TAGS:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_INVALID_URL_PROTOCOL:
       return 54;
-    case amp.validator.ValidationError.Code.DISALLOWED_CHILD_TAG_NAME:
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_DISALLOWED_RELATIVE_URL:
       return 55;
-    case amp.validator.ValidationError.Code.DISALLOWED_FIRST_CHILD_TAG_NAME:
+    case amp.validator.ValidationError.Code.INCORRECT_NUM_CHILD_TAGS:
       return 56;
-    case amp.validator.ValidationError.Code.CSS_SYNTAX_INVALID_ATTR_SELECTOR:
+    case amp.validator.ValidationError.Code.DISALLOWED_CHILD_TAG_NAME:
       return 57;
+    case amp.validator.ValidationError.Code.DISALLOWED_FIRST_CHILD_TAG_NAME:
+      return 58;
+    case amp.validator.ValidationError.Code.CSS_SYNTAX_INVALID_ATTR_SELECTOR:
+      return 59;
     case amp.validator.ValidationError.Code.GENERAL_DISALLOWED_TAG:
       return 100;
     case amp.validator.ValidationError.Code.DEPRECATED_ATTR:
@@ -2953,7 +3014,8 @@ class ParsedValidatorRules {
 
     for (let i = 0; i < rules.tags.length; ++i) {
       const tag = rules.tags[i];
-      goog.asserts.assert(rules.templateSpecUrl != null);
+      if (amp.validator.GENERATE_DETAILED_ERRORS)
+        goog.asserts.assert(rules.templateSpecUrl != null);
       const parsedTagSpec = new ParsedTagSpec(
           rules.templateSpecUrl, parsedAttrLists, tagspecIdsByTagSpecName,
           shouldRecordTagspecValidated(tag, tagSpecNamesToTrack), tag, i);
diff --git a/validator/validator.proto b/validator/validator.proto
index 7998910a8595..e3681dc69a53 100644
--- a/validator/validator.proto
+++ b/validator/validator.proto
@@ -56,6 +56,8 @@ message UrlSpec {
   optional bool allow_relative = 2 [default = true];
   // Whether the empty string '' is allowed for this URL value.
   optional bool allow_empty = 3;
+  // Must be lowercase.
+  repeated string disallowed_domain = 4;
 }
 
 // Attributes that are not covered by at least one of these specs are
@@ -388,7 +390,7 @@ message ValidationError {
     DEV_WARNING = 3; // DEPRECATED DO NOT USE.
   }
   optional Severity severity = 6 [ default = ERROR ];
-  // NEXT AVAILABLE TAG: 62
+  // NEXT AVAILABLE TAG: 64
   enum Code {
     UNKNOWN_CODE = 0;
     MANDATORY_TAG_MISSING = 1;
@@ -418,6 +420,7 @@ message ValidationError {
     MISSING_URL = 35;
     INVALID_URL = 36;
     INVALID_URL_PROTOCOL = 37;
+    DISALLOWED_DOMAIN = 62;
     DISALLOWED_RELATIVE_URL = 49;
     DISALLOWED_PROPERTY_IN_ATTR_VALUE = 16;
     MUTUALLY_EXCLUSIVE_ATTRS = 17;
@@ -450,6 +453,7 @@ message ValidationError {
     CSS_SYNTAX_MISSING_URL = 52;
     CSS_SYNTAX_INVALID_URL = 53;
     CSS_SYNTAX_INVALID_URL_PROTOCOL = 54;
+    CSS_SYNTAX_DISALLOWED_DOMAIN = 63;
     CSS_SYNTAX_DISALLOWED_RELATIVE_URL = 55;
     CSS_SYNTAX_INVALID_ATTR_SELECTOR = 59;
   }