diff --git a/extensions/amp-date-display/0.1/test/validator-amp-date-display.out b/extensions/amp-date-display/0.1/test/validator-amp-date-display.out
index 1ee8ec400073..c3f49a4f10ec 100644
--- a/extensions/amp-date-display/0.1/test/validator-amp-date-display.out
+++ b/extensions/amp-date-display/0.1/test/validator-amp-date-display.out
@@ -188,4 +188,4 @@ amp-date-display/0.1/test/validator-amp-date-display.html:169:2 The attribute 'd
 |    </amp-date-display>
 |  </body>
 |
-|  </html>
\ No newline at end of file
+|  </html>
diff --git a/extensions/amp-script/0.1/test/validator-amp-script.out b/extensions/amp-script/0.1/test/validator-amp-script.out
index 007d8d99ae1a..de4769bf4791 100644
--- a/extensions/amp-script/0.1/test/validator-amp-script.out
+++ b/extensions/amp-script/0.1/test/validator-amp-script.out
@@ -112,4 +112,4 @@ amp-script/0.1/test/validator-amp-script.html:84:2 Custom JavaScript is not allo
 amp-script/0.1/test/validator-amp-script.html:89:2 Custom JavaScript is not allowed. (see https://amp.dev/documentation/guides-and-tutorials/learn/spec/amphtml#html-tags) [CUSTOM_JAVASCRIPT_DISALLOWED]
 |      document.body.textContent = "Hello World!";
 |    </script>
-|  </body>
\ No newline at end of file
+|  </body>
diff --git a/validator/engine/validator.js b/validator/engine/validator.js
index 87f89265a7b3..c5586ac78aa3 100644
--- a/validator/engine/validator.js
+++ b/validator/engine/validator.js
@@ -1518,7 +1518,7 @@ class TagStack {
   }
 
   /**
-   * Records that tag currently on the stack is using ampdevmode.
+   * Records that tag currently on the stack is using data-ampdevmode.
    */
   setDevMode() {
     this.back_().devMode = true;
@@ -2741,11 +2741,11 @@ class Context {
   }
 
   /**
-   * Returns true iff "ampdevmode" is a type identifier in this document.
+   * Returns true iff "data-ampdevmode" is a type identifier in this document.
    * @return {boolean}
    */
   isDevMode() {
-    return this.typeIdentifiers_.includes('ampdevmode');
+    return this.typeIdentifiers_.includes('data-ampdevmode');
   }
 
   /**
@@ -4252,19 +4252,19 @@ function validateAttrDeclaration(
 
 /**
  * Returns true if errors reported on this tag should be suppressed, due to
- * ampdevmode annotations.
+ * data-ampdevmode annotations.
  * @param {!amp.htmlparser.ParsedHtmlTag} encounteredTag
  * @param {!Context} context
  * @return {boolean}
  */
 function ShouldSuppressDevModeErrors(encounteredTag, context) {
   if (!context.isDevMode()) return false;
-  // Cannot suppress errors on HTML tag. The "ampdevmode" here is a
+  // Cannot suppress errors on HTML tag. The "data-ampdevmode" here is a
   // type identifier. Suppressing errors here would suppress all errors since
   // HTML is the root of the document.
   if (encounteredTag.upperName() === 'HTML') return false;
   for (const attr of encounteredTag.attrs()) {
-    if (attr.name === 'ampdevmode') return true;
+    if (attr.name === 'data-ampdevmode') return true;
   }
   return context.getTagStack().isDevMode();
 }
@@ -4979,7 +4979,7 @@ class ParsedValidatorRules {
     this.typeIdentifiers_['amp4email'] = 0;
     this.typeIdentifiers_['actions'] = 0;
     this.typeIdentifiers_['transformed'] = 0;
-    this.typeIdentifiers_['ampdevmode'] = 0;
+    this.typeIdentifiers_['data-ampdevmode'] = 0;
 
     /**
      * @type {function(!amp.validator.TagSpec) : boolean}
@@ -5191,7 +5191,7 @@ class ParsedValidatorRules {
           // mandatory unlike other type identifiers.
           if (typeIdentifier !== 'actions' &&
               typeIdentifier !== 'transformed' &&
-              typeIdentifier !== 'ampdevmode') {
+              typeIdentifier !== 'data-ampdevmode') {
             hasMandatoryTypeIdentifier = true;
           }
           // The type identifier "transformed" has restrictions on it's value.
@@ -5209,7 +5209,7 @@ class ParsedValidatorRules {
                   validationResult);
             }
           }
-          if (typeIdentifier === 'ampdevmode') {
+          if (typeIdentifier === 'data-ampdevmode') {
             // https://github.com/ampproject/amphtml/issues/20974
             // We always emit an error for this type identifier, but it
             // suppresses other errors later in the document.
@@ -5248,23 +5248,23 @@ class ParsedValidatorRules {
     switch (this.htmlFormat_) {
       case 'AMP':
         this.validateTypeIdentifiers(
-            htmlTag.attrs(), ['⚡', 'amp', 'transformed', 'ampdevmode'], context,
-            validationResult);
+            htmlTag.attrs(), ['⚡', 'amp', 'transformed', 'data-ampdevmode'],
+            context, validationResult);
         break;
       case 'AMP4ADS':
         this.validateTypeIdentifiers(
-            htmlTag.attrs(), ['⚡4ads', 'amp4ads', 'ampdevmode'], context,
+            htmlTag.attrs(), ['⚡4ads', 'amp4ads', 'data-ampdevmode'], context,
             validationResult);
         break;
       case 'AMP4EMAIL':
         this.validateTypeIdentifiers(
-            htmlTag.attrs(), ['⚡4email', 'amp4email', 'ampdevmode'], context,
-            validationResult);
+            htmlTag.attrs(), ['⚡4email', 'amp4email', 'data-ampdevmode'],
+            context, validationResult);
         break;
       case 'ACTIONS':
         this.validateTypeIdentifiers(
-            htmlTag.attrs(), ['⚡', 'amp', 'actions', 'ampdevmode'], context,
-            validationResult);
+            htmlTag.attrs(), ['⚡', 'amp', 'actions', 'data-ampdevmode'],
+            context,  validationResult);
         if (validationResult.typeIdentifier.indexOf('actions') === -1) {
           context.addError(
               amp.validator.ValidationError.Code.MANDATORY_ATTR_MISSING,
diff --git a/validator/testdata/feature_tests/dev_mode.html b/validator/testdata/feature_tests/dev_mode.html
index efe020557779..6a563d390a6a 100644
--- a/validator/testdata/feature_tests/dev_mode.html
+++ b/validator/testdata/feature_tests/dev_mode.html
@@ -15,15 +15,15 @@
 -->
 <!--
   Test Description:
-  This tests the logic for ampdevmode attributes.
+  This tests the logic for data-ampdevmode attributes.
   See https://github.com/ampproject/amphtml/issues/20974 for the
   original motivation. The idea is that an author can tag a document with
-  the ampdevmode type identifier, which will emit an error and make
+  the data-ampdevmode type identifier, which will emit an error and make
   the document invalid. However, any other tags marked with the same
   identifier will no longer emit errors, regardless of the error type.
 -->
 <!doctype html>
-<html ⚡ ampdevmode>
+<html ⚡ data-ampdevmode>
 <head>
   <meta charset="utf-8">
   <link rel="canonical" href="./regular-html-version.html">
@@ -38,17 +38,17 @@
   <faketag></faketag>
   <anotherfaketag></anotherfaketag>
 
-  <!-- Tagged with ampdevmode, so errors are suppressed. -->
-  <faketag ampdevmode></faketag>
+  <!-- Tagged with data-ampdevmode, so errors are suppressed. -->
+  <faketag data-ampdevmode></faketag>
 
   <!-- Also suppresses the entire tree. -->
-  <faketag ampdevmode>
+  <faketag data-ampdevmode>
     <anotherfaketag></anotherfaketag>
   </faketag>
 
   <!-- Yet, it does not prevent the tag from satisfying conditions, such as
        the amp-autocomplete-0.1.js being used -->
-  <amp-autocomplete ampdevmode></amp-autocomplete>
+  <amp-autocomplete data-ampdevmode></amp-autocomplete>
 
 </body>
 </html>
diff --git a/validator/testdata/feature_tests/dev_mode.out b/validator/testdata/feature_tests/dev_mode.out
index 4e63aa8782d3..b8a42305f2e2 100644
--- a/validator/testdata/feature_tests/dev_mode.out
+++ b/validator/testdata/feature_tests/dev_mode.out
@@ -16,17 +16,17 @@ FAIL
 |  -->
 |  <!--
 |    Test Description:
-|    This tests the logic for ampdevmode attributes.
+|    This tests the logic for data-ampdevmode attributes.
 |    See https://github.com/ampproject/amphtml/issues/20974 for the
 |    original motivation. The idea is that an author can tag a document with
-|    the ampdevmode type identifier, which will emit an error and make
+|    the data-ampdevmode type identifier, which will emit an error and make
 |    the document invalid. However, any other tags marked with the same
 |    identifier will no longer emit errors, regardless of the error type.
 |  -->
 |  <!doctype html>
-|  <html ⚡ ampdevmode>
+|  <html ⚡ data-ampdevmode>
 >> ^~~~~~~~~
-feature_tests/dev_mode.html:26:0 Tag 'html' marked with attribute 'ampdevmode'. Validator will suppress errors regarding any other tag with this attribute. [GENERIC]
+feature_tests/dev_mode.html:26:0 Tag 'html' marked with attribute 'data-ampdevmode'. Validator will suppress errors regarding any other tag with this attribute. [GENERIC]
 |  <head>
 |    <meta charset="utf-8">
 |    <link rel="canonical" href="./regular-html-version.html">
@@ -45,17 +45,17 @@ feature_tests/dev_mode.html:38:2 The tag 'faketag' is disallowed. [DISALLOWED_HT
 >>   ^~~~~~~~~
 feature_tests/dev_mode.html:39:2 The tag 'anotherfaketag' is disallowed. [DISALLOWED_HTML]
 |
-|    <!-- Tagged with ampdevmode, so errors are suppressed. -->
-|    <faketag ampdevmode></faketag>
+|    <!-- Tagged with data-ampdevmode, so errors are suppressed. -->
+|    <faketag data-ampdevmode></faketag>
 |
 |    <!-- Also suppresses the entire tree. -->
-|    <faketag ampdevmode>
+|    <faketag data-ampdevmode>
 |      <anotherfaketag></anotherfaketag>
 |    </faketag>
 |
 |    <!-- Yet, it does not prevent the tag from satisfying conditions, such as
 |         the amp-autocomplete-0.1.js being used -->
-|    <amp-autocomplete ampdevmode></amp-autocomplete>
+|    <amp-autocomplete data-ampdevmode></amp-autocomplete>
 |
 |  </body>
 |  </html>
diff --git a/validator/testdata/feature_tests/no_dev_mode.html b/validator/testdata/feature_tests/no_dev_mode.html
index 731f268babe8..cee3f6ad8d4a 100644
--- a/validator/testdata/feature_tests/no_dev_mode.html
+++ b/validator/testdata/feature_tests/no_dev_mode.html
@@ -15,15 +15,15 @@
 -->
 <!--
   Test Description:
-  This tests the logic for ampdevmode attributes.
+  This tests the logic for data-ampdevmode attributes.
   See https://github.com/ampproject/amphtml/issues/20974 for the
   original motivation. The idea is that an author can tag a document with
-  the ampdevmode type identifier, which will emit an error and make
+  the data-ampdevmode type identifier, which will emit an error and make
   the document invalid. However, any other tags marked with the same
   identifier will no longer emit errors, regardless of the error type.
 
   Unlike dev_mode.html, this test does not enable dev mode, and should emit
-  full errors. Other than the lack of `ampdevmode` in the <html> tag,
+  full errors. Other than the lack of `data-ampdevmode` in the <html> tag,
   and some comments, this is the same as dev_mode.html.
 -->
 <!doctype html>
@@ -42,14 +42,14 @@
   <faketag></faketag>
   <anotherfaketag></anotherfaketag>
 
-  <!-- Tagged with ampdevmode, but not dev mode in html tag. -->
-  <faketag ampdevmode></faketag>
+  <!-- Tagged with data-ampdevmode, but not dev mode in html tag. -->
+  <faketag data-ampdevmode></faketag>
 
-  <faketag ampdevmode>
+  <faketag data-ampdevmode>
     <anotherfaketag></anotherfaketag>
   </faketag>
 
-  <amp-autocomplete ampdevmode></amp-autocomplete>
+  <amp-autocomplete data-ampdevmode></amp-autocomplete>
 
 </body>
 </html>
diff --git a/validator/testdata/feature_tests/no_dev_mode.out b/validator/testdata/feature_tests/no_dev_mode.out
index 533de875f5e0..1afc23bcfd4c 100644
--- a/validator/testdata/feature_tests/no_dev_mode.out
+++ b/validator/testdata/feature_tests/no_dev_mode.out
@@ -16,15 +16,15 @@ FAIL
 |  -->
 |  <!--
 |    Test Description:
-|    This tests the logic for ampdevmode attributes.
+|    This tests the logic for data-ampdevmode attributes.
 |    See https://github.com/ampproject/amphtml/issues/20974 for the
 |    original motivation. The idea is that an author can tag a document with
-|    the ampdevmode type identifier, which will emit an error and make
+|    the data-ampdevmode type identifier, which will emit an error and make
 |    the document invalid. However, any other tags marked with the same
 |    identifier will no longer emit errors, regardless of the error type.
 |
 |    Unlike dev_mode.html, this test does not enable dev mode, and should emit
-|    full errors. Other than the lack of `ampdevmode` in the <html> tag,
+|    full errors. Other than the lack of `data-ampdevmode` in the <html> tag,
 |    and some comments, this is the same as dev_mode.html.
 |  -->
 |  <!doctype html>
@@ -47,12 +47,12 @@ feature_tests/no_dev_mode.html:42:2 The tag 'faketag' is disallowed. [DISALLOWED
 >>   ^~~~~~~~~
 feature_tests/no_dev_mode.html:43:2 The tag 'anotherfaketag' is disallowed. [DISALLOWED_HTML]
 |
-|    <!-- Tagged with ampdevmode, but not dev mode in html tag. -->
-|    <faketag ampdevmode></faketag>
+|    <!-- Tagged with data-ampdevmode, but not dev mode in html tag. -->
+|    <faketag data-ampdevmode></faketag>
 >>   ^~~~~~~~~
 feature_tests/no_dev_mode.html:46:2 The tag 'faketag' is disallowed. [DISALLOWED_HTML]
 |
-|    <faketag ampdevmode>
+|    <faketag data-ampdevmode>
 >>   ^~~~~~~~~
 feature_tests/no_dev_mode.html:48:2 The tag 'faketag' is disallowed. [DISALLOWED_HTML]
 |      <anotherfaketag></anotherfaketag>
@@ -60,9 +60,7 @@ feature_tests/no_dev_mode.html:48:2 The tag 'faketag' is disallowed. [DISALLOWED
 feature_tests/no_dev_mode.html:49:4 The tag 'anotherfaketag' is disallowed. [DISALLOWED_HTML]
 |    </faketag>
 |
-|    <amp-autocomplete ampdevmode></amp-autocomplete>
->>   ^~~~~~~~~
-feature_tests/no_dev_mode.html:52:2 The attribute 'ampdevmode' may not appear in tag 'amp-autocomplete'. (see https://amp.dev/documentation/components/amp-autocomplete) [DISALLOWED_HTML]
+|    <amp-autocomplete data-ampdevmode></amp-autocomplete>
 |
 |  </body>
 |  </html>
diff --git a/validator/validator-main.protoascii b/validator/validator-main.protoascii
index 37ad617d235f..d12d31de7305 100644
--- a/validator/validator-main.protoascii
+++ b/validator/validator-main.protoascii
@@ -26,7 +26,7 @@ min_validator_revision_required: 375
 # 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: 936
+spec_file_revision: 945
 
 styles_spec_url: "https://amp.dev/documentation/guides-and-tutorials/develop/style_and_layout/style_pages"
 script_spec_url: "https://amp.dev/documentation/guides-and-tutorials/learn/spec/amphtml#html-tags"
@@ -310,6 +310,7 @@ tags: {
   spec_name: "link rel=stylesheet for fonts"
   named_id: LINK_FONT_STYLESHEET
   mandatory_parent: "HEAD"
+  attr_lists: "nonce-attr"
   attrs: { name: "async" }
   attrs: { name: "crossorigin" }  # SRI attribute (https://www.w3.org/TR/SRI/)
   attrs: {
@@ -7348,6 +7349,6 @@ error_formats {
 }
 error_formats {
   code: DEV_MODE_ONLY
-  format: "Tag 'html' marked with attribute 'ampdevmode'. Validator "
+  format: "Tag 'html' marked with attribute 'data-ampdevmode'. Validator "
           "will suppress errors regarding any other tag with this attribute."
 }