diff --git a/.circleci/install_validator_dependencies.sh b/.circleci/install_validator_dependencies.sh
index e6e13bbcd490..8ebc5f94a164 100755
--- a/.circleci/install_validator_dependencies.sh
+++ b/.circleci/install_validator_dependencies.sh
@@ -13,7 +13,7 @@ sudo mv bazel.gpg /etc/apt/trusted.gpg.d/
 echo "deb [arch=amd64] https://storage.googleapis.com/bazel-apt stable jdk1.8" | sudo tee /etc/apt/sources.list.d/bazel.list
 
 echo $(GREEN "Updating and installing apt packages...")
-sudo apt update && sudo apt install bazel-5.4.0 clang python3 python3-pip protobuf-compiler
+sudo apt update && sudo apt install bazel-7.1.0 clang python3 python3-pip protobuf-compiler
 
 echo $(GREEN "Installing protobuf python module...")
 pip3 install protobuf==3.19.4
diff --git a/build-system/tasks/validator.js b/build-system/tasks/validator.js
index 405d18c0939f..8591431265e9 100644
--- a/build-system/tasks/validator.js
+++ b/build-system/tasks/validator.js
@@ -25,7 +25,7 @@ async function validator() {
  */
 async function validatorCpp() {
   const bazelCmd = [
-    'bazel-5.4.0 test',
+    'bazel-7.1.0 test',
     '--repo_env=CC=clang',
     "--cxxopt='-std=c++17'",
     '--discard_analysis_cache',
diff --git a/validator/cpp/engine/BUILD b/validator/cpp/engine/BUILD
index c60425d0d25c..5b4705354473 100644
--- a/validator/cpp/engine/BUILD
+++ b/validator/cpp/engine/BUILD
@@ -1,6 +1,7 @@
 load("@rules_cc//cc:defs.bzl", "cc_library", "cc_test")
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
 load("embed_data.bzl", "embed_data")
+load("//tools/build_defs/license:license.bzl", "license")
 
 # Requirements:
 # clang with c++17 support.
@@ -14,7 +15,15 @@ load("embed_data.bzl", "embed_data")
 #
 # bazel test --cxxopt='-std=c++17' validator_test
 
-package(default_visibility = ["//visibility:public"])
+package(
+    default_applicable_licenses = [":license"],
+    default_visibility = ["//visibility:public"],
+)
+
+license(
+    name = "license",
+    package_name = "ampvalidator",
+)
 
 licenses(["notice"])
 
diff --git a/validator/cpp/engine/validator-internal.cc b/validator/cpp/engine/validator-internal.cc
index 63856a5eb540..799563cd4fb2 100644
--- a/validator/cpp/engine/validator-internal.cc
+++ b/validator/cpp/engine/validator-internal.cc
@@ -595,7 +595,7 @@ class ParsedAttrSpec {
     return value_property_by_name_;
   }
 
-  const unordered_map<std::string, const CssDeclaration*>&
+  const absl::flat_hash_map<std::string, const CssDeclaration*>&
   css_declaration_by_name() const {
     return css_declaration_by_name_;
   }
@@ -620,7 +620,8 @@ class ParsedAttrSpec {
   // Name lookup for spec().value_properties().properties().
   unordered_map<std::string, const PropertySpec*> value_property_by_name_;
   // Name lookup for spec().css_declaration().
-  unordered_map<std::string, const CssDeclaration*> css_declaration_by_name_;
+  absl::flat_hash_map<std::string, const CssDeclaration*>
+      css_declaration_by_name_;
   // The mandatory spec().value_properties().properties().
   vector<const PropertySpec*> mandatory_value_properties_;
   vector<TypeIdentifier> disabled_by_;
@@ -4323,7 +4324,7 @@ void ValidateAttrDeclaration(const ParsedAttrSpec& parsed_attr_spec,
   // If there were errors parsing, exit from validating further.
   if (!css_errors.empty()) return;
 
-  const unordered_map<std::string, const CssDeclaration*>&
+  const absl::flat_hash_map<std::string, const CssDeclaration*>&
       css_declaration_by_name = parsed_attr_spec.css_declaration_by_name();
 
   for (auto& declaration : declarations) {
diff --git a/validator/cpp/engine/validator_test.cc b/validator/cpp/engine/validator_test.cc
index 545f14abbe59..491684ede86c 100644
--- a/validator/cpp/engine/validator_test.cc
+++ b/validator/cpp/engine/validator_test.cc
@@ -1220,7 +1220,8 @@ TEST(ValidatorTest, RulesMakeSense) {
                         HtmlFormat::UNKNOWN_CODE),
               html_format.cend())
         << "tagSpec.htmlFormat should never contain UNKNOWN_CODE"
-        << ":\n" << tag_spec.DebugString();
+        << ":\n"
+        << tag_spec;
 
     EXPECT_TRUE(tag_spec.has_tag_name());
     EXPECT_TRUE(RE2::PartialMatch(tag_spec.tag_name(), tag_name_regex));
@@ -1562,12 +1563,12 @@ TEST(ValidatorTest, RulesMakeSense) {
     }
 
     for (const auto& attr_spec : tag_spec.attrs()) {
-      EXPECT_TRUE(attr_spec.has_name()) << attr_spec.DebugString();
+      EXPECT_TRUE(attr_spec.has_name()) << attr_spec;
       // Attribute Spec names are matched against lowercased attributes,
       // so the rules *must* also be lower case or non-cased.
       EXPECT_TRUE(RE2::FullMatch(attr_spec.name(), RE2("[^A-Z]+")))
-          << attr_spec.DebugString();
-      EXPECT_NE(attr_spec.name(), "[style]") << attr_spec.DebugString();
+          << attr_spec;
+      EXPECT_NE(attr_spec.name(), "[style]") << attr_spec;
       if (attr_spec.has_value_url()) {
         for (const std::string& protocol : attr_spec.value_url().protocol()) {
           // UrlSpec protocol is matched against lowercased protocol names,
@@ -1582,27 +1583,24 @@ TEST(ValidatorTest, RulesMakeSense) {
             if (protocol == "http" &&
                 attr_spec.value_url().has_allow_relative()) {
               EXPECT_TRUE(attr_spec.value_url().allow_relative())
-                  << attr_spec.value_url().DebugString();
+                  << attr_spec.value_url();
             }
           }
         }
       }
       if (attr_spec.has_value_regex()) {
-        EXPECT_TRUE(RE2(attr_spec.value_regex()).ok())
-            << attr_spec.DebugString();
+        EXPECT_TRUE(RE2(attr_spec.value_regex()).ok()) << attr_spec;
       }
       if (attr_spec.has_value_regex_casei()) {
-        EXPECT_TRUE(RE2(attr_spec.value_regex_casei()).ok())
-            << attr_spec.DebugString();
+        EXPECT_TRUE(RE2(attr_spec.value_regex_casei()).ok()) << attr_spec;
       }
       if (attr_spec.has_disallowed_value_regex()) {
-        EXPECT_TRUE(RE2(attr_spec.disallowed_value_regex()).ok())
-            << attr_spec.DebugString();
+        EXPECT_TRUE(RE2(attr_spec.disallowed_value_regex()).ok()) << attr_spec;
       }
       if (attr_spec.has_value_url()) {
         EXPECT_GT(attr_spec.value_url().protocol().size(), 0)
             << "value_url must have at least one protocol\n"
-            << attr_spec.DebugString();
+            << attr_spec;
       }
       int num_values = 0;
       if (!attr_spec.value().empty()) {
@@ -1627,12 +1625,12 @@ TEST(ValidatorTest, RulesMakeSense) {
       if (attr_spec.name() == "id" && num_values == 0) {
         EXPECT_TRUE(attr_spec.has_disallowed_value_regex())
             << "'id' attribute must have 'disallowed_value_regex' set\n"
-            << attr_spec.DebugString();
+            << attr_spec;
       }
       if (attr_spec.name() == "name" && num_values == 0) {
         EXPECT_TRUE(attr_spec.has_disallowed_value_regex())
             << "'name' attribute must have 'disallowed_value_regex' set\n"
-            << attr_spec.DebugString();
+            << attr_spec;
       }
       if (attr_spec.has_deprecation()) {
         EXPECT_TRUE(attr_spec.has_deprecation_url());
diff --git a/validator/cpp/htmlparser/BUILD b/validator/cpp/htmlparser/BUILD
index 78de2920159d..61f4e2958f1e 100644
--- a/validator/cpp/htmlparser/BUILD
+++ b/validator/cpp/htmlparser/BUILD
@@ -195,10 +195,10 @@ cc_library(
     hdrs = [
         "logging.h",
     ],
+    copts = ["-std=c++17"],
     deps = [
         ":glog_polyfill",
     ],
-    copts = ["-std=c++17"],
 )
 
 # Defines token type and token structures, used during tokenization.
@@ -551,7 +551,7 @@ cc_test(
         ":strings",
         ":testconstants",
         ":tokenizer",
-        "@com_google_googletest//:gtest_main",
         "@com_google_absl//absl/flags:flag",
+        "@com_google_googletest//:gtest_main",
     ],
 )
diff --git a/validator/cpp/htmlparser/allocator.h b/validator/cpp/htmlparser/allocator.h
index 0620c4ed32fb..913e3befbb5c 100644
--- a/validator/cpp/htmlparser/allocator.h
+++ b/validator/cpp/htmlparser/allocator.h
@@ -138,7 +138,7 @@
 // IMPORTANT: Tree like structure must not destroy the child nodes or sibling
 // nodes. Allocator destroys all the objects and call its destructor, it is an
 // error to invoke destructors on objects allocated by this allocator. Allocator
-// is the master owner of all the objects. Client treats all objects as const
+// is the primary owner of all the objects. Client treats all objects as const
 // pointer as far as destruction goes.
 //
 // It is not possible to destroy random objects or free up the slots to be
@@ -174,6 +174,7 @@
 #include <cstring>
 #include <memory>
 #include <tuple>
+#include <type_traits>
 #include <vector>
 
 namespace htmlparser {
diff --git a/validator/cpp/htmlparser/allocator_test.cc b/validator/cpp/htmlparser/allocator_test.cc
index 7922016aafca..3f20071b1017 100644
--- a/validator/cpp/htmlparser/allocator_test.cc
+++ b/validator/cpp/htmlparser/allocator_test.cc
@@ -1,5 +1,10 @@
 #include "cpp/htmlparser/allocator.h"
 
+#include <array>
+#include <cstdint>
+#include <string>
+#include <vector>
+
 #include "gtest/gtest.h"
 
 // Memory leaks will automatically be detected by the test framework.
@@ -12,9 +17,9 @@ TEST(AllocatorTest, BasicTest) {
     int32_t a;
     int64_t b;
     std::string c;
-    short d;
+    uint16_t d;
     Data() {}
-    Data(int32_t a_, int64_t b_, std::string c_, short d_)
+    Data(int32_t a_, int64_t b_, std::string c_, uint16_t d_)
         : a(a_), b(b_), c(c_), d(d_) {}
   };
 
@@ -146,7 +151,7 @@ TEST(AllocatorTest, DestructorCalled) {
 
 TEST(AllocatorTest, BitFields) {
   struct HasBitFields {
-    short s;
+    uint16_t s;
     char c;
     int flip : 1;
     int nybble : 4;
diff --git a/validator/cpp/htmlparser/atomutil.cc b/validator/cpp/htmlparser/atomutil.cc
index 368b32848ebd..a5e1771aa7de 100644
--- a/validator/cpp/htmlparser/atomutil.cc
+++ b/validator/cpp/htmlparser/atomutil.cc
@@ -1,5 +1,8 @@
 #include "cpp/htmlparser/atomutil.h"
 
+#include <string>
+#include <string_view>
+
 #include "cpp/htmlparser/hash.h"
 
 namespace htmlparser {
@@ -20,7 +23,7 @@ Atom AtomUtil::ToAtom(const std::string& s) {
   table_index = (hash >> 16) & (kNamesHashTable.size() - 1);
   atom_value = kNamesHashTable[table_index];
   atom_len = atom_value & 0xff;
-  if (atom_len == s.size() && ToString(atom_value).compare(s) == 0) {
+  if (atom_len == s.size() && ToString(atom_value) == s) {
     return CastToAtom(atom_value);
   }
 
diff --git a/validator/cpp/htmlparser/bin/atomgen.cc b/validator/cpp/htmlparser/bin/atomgen.cc
index 54a41ab09934..9546f4dc0efb 100644
--- a/validator/cpp/htmlparser/bin/atomgen.cc
+++ b/validator/cpp/htmlparser/bin/atomgen.cc
@@ -13,6 +13,7 @@
 #include <memory>
 #include <sstream>
 #include <string>
+#include <string_view>
 #include <utility>
 #include <vector>
 
@@ -55,12 +56,12 @@ class TableBuilder {
 
   bool Insert(const std::string& s) {
     std::pair<uint32_t, uint32_t> hashes = Hash(s);
-    if (table_[hashes.first] == "") {
+    if (table_[hashes.first].empty()) {
       table_[hashes.first] = s;
       return true;
     }
 
-    if (table_[hashes.second] == "") {
+    if (table_[hashes.second].empty()) {
       table_[hashes.second] = s;
       return true;
     }
@@ -100,7 +101,7 @@ class TableBuilder {
     std::pair<uint32_t, uint32_t> hashes = Hash(entry);
     uint32_t new_location = hashes.first + hashes.second - i;
 
-    if (table_[new_location] != "" && !Push(new_location, depth + 1)) {
+    if (!table_[new_location].empty() && !Push(new_location, depth + 1)) {
       return false;
     }
 
@@ -190,8 +191,8 @@ int main(int argc, char** argv) {
   // Find hash that minimizes table size.
   std::unique_ptr<TableBuilder> table{nullptr};
   for (int i = 0; i < 1; i++) {
-    if (table.get() != nullptr
-        && (1 << (table->hash_num_bits() - 1)) < all_names.size()) {
+    if (table != nullptr &&
+        (1 << (table->hash_num_bits() - 1)) < all_names.size()) {
       break;
     }
 
@@ -199,8 +200,7 @@ int main(int argc, char** argv) {
     uint32_t rand_state;
     uint32_t hash0 = rand_r(&rand_state) % 1000000000;
     for (uint32_t k = 0; k <= 16; k++) {
-      if (table.get() != nullptr && k >= table->hash_num_bits())
-        break;
+      if (table != nullptr && k >= table->hash_num_bits()) break;
       std::unique_ptr<TableBuilder> base(new TableBuilder());
       if (base->Init(hash0, k, all_names)) {
         table.reset(base.release());
@@ -209,7 +209,7 @@ int main(int argc, char** argv) {
     }
   }
 
-  if (table.get() == nullptr) {
+  if (table == nullptr) {
     std::cerr << "Failed to construct string table." << std::endl;
     std::cerr <<  all_names.size() << ": elements." << std::endl;
     return EXIT_FAILURE;
@@ -224,11 +224,11 @@ int main(int argc, char** argv) {
   while (changed) {
     changed = false;
     for (std::size_t i = 0; i < layout.size(); i++) {
-      if (layout[i] == "") continue;
+      if (layout[i].empty()) continue;
 
       for (std::size_t j = 0; j < layout.size(); j++) {
-        if (i != j && layout[j] != ""
-            && layout[i].find(layout[j]) != std::string::npos) {
+        if (i != j && !layout[j].empty() &&
+            layout[i].find(layout[j]) != std::string::npos) {
           changed = true;
           layout[j] = "";
         }
@@ -244,7 +244,7 @@ int main(int argc, char** argv) {
     int bestj = -1;
     int bestk = 0;
     for (std::size_t i = 0; i < layout.size(); i++) {
-      if (layout[i] == "") continue;
+      if (layout[i].empty()) continue;
 
       for (std::size_t j = 0; j < layout.size(); j++) {
         if (i == j) continue;
diff --git a/validator/cpp/htmlparser/bin/casetablegen.cc b/validator/cpp/htmlparser/bin/casetablegen.cc
index a66464dc2bda..ad93231e961d 100644
--- a/validator/cpp/htmlparser/bin/casetablegen.cc
+++ b/validator/cpp/htmlparser/bin/casetablegen.cc
@@ -1,7 +1,9 @@
 #include <fstream>
 #include <iostream>
 #include <sstream>
+#include <string>
 #include <utility>
+#include <vector>
 
 #include "cpp/htmlparser/defer.h"
 #include "cpp/htmlparser/fileutil.h"
diff --git a/validator/cpp/htmlparser/bin/entitytablegen.cc b/validator/cpp/htmlparser/bin/entitytablegen.cc
index 95810636a429..050dfffdebee 100644
--- a/validator/cpp/htmlparser/bin/entitytablegen.cc
+++ b/validator/cpp/htmlparser/bin/entitytablegen.cc
@@ -6,6 +6,7 @@
 #include <fstream>
 #include <iostream>
 #include <sstream>
+#include <string>
 #include <utility>
 #include <vector>
 
diff --git a/validator/cpp/htmlparser/bin/validatorgen.cc b/validator/cpp/htmlparser/bin/validatorgen.cc
index 8300004437ce..934938d85c29 100644
--- a/validator/cpp/htmlparser/bin/validatorgen.cc
+++ b/validator/cpp/htmlparser/bin/validatorgen.cc
@@ -15,6 +15,7 @@
 //
 
 #include <iostream>
+#include <string>
 
 #include "glog/logging.h"
 #include "absl/flags/flag.h"
diff --git a/validator/cpp/htmlparser/casetable_test.cc b/validator/cpp/htmlparser/casetable_test.cc
index ed20806894b3..fdffbb65a704 100644
--- a/validator/cpp/htmlparser/casetable_test.cc
+++ b/validator/cpp/htmlparser/casetable_test.cc
@@ -1,5 +1,7 @@
 #include "cpp/htmlparser/casetable.h"
 
+#include <string_view>
+
 #include "gtest/gtest.h"
 #include "cpp/htmlparser/strings.h"
 
diff --git a/validator/cpp/htmlparser/css/amp4ads-parse-css.cc b/validator/cpp/htmlparser/css/amp4ads-parse-css.cc
index 0fec958bcd1d..5072494d3a42 100644
--- a/validator/cpp/htmlparser/css/amp4ads-parse-css.cc
+++ b/validator/cpp/htmlparser/css/amp4ads-parse-css.cc
@@ -1,13 +1,14 @@
 #include "cpp/htmlparser/css/amp4ads-parse-css.h"
 
-#include "absl/memory/memory.h"
+#include <memory>
+#include <string>
+#include <vector>
+
 #include "absl/strings/str_cat.h"
 #include "absl/strings/str_join.h"
 #include "cpp/htmlparser/css/parse-css.h"
 #include "re2/re2.h"
 
-using absl::make_unique;
-using std::string_view;
 using amp::validator::ValidationError;
 using std::unique_ptr;
 
@@ -18,7 +19,7 @@ namespace {
 unique_ptr<ErrorToken> CreateParseErrorTokenAt(
     const Token& position_token, ValidationError::Code code,
     const std::vector<std::string>& params) {
-  auto token = make_unique<ErrorToken>(code, params);
+  auto token = std::make_unique<ErrorToken>(code, params);
   position_token.CopyStartPositionTo(token.get());
   return token;
 }
diff --git a/validator/cpp/htmlparser/css/parse-css-urls.cc b/validator/cpp/htmlparser/css/parse-css-urls.cc
index 9d2ae3d3033d..9e029a376a26 100644
--- a/validator/cpp/htmlparser/css/parse-css-urls.cc
+++ b/validator/cpp/htmlparser/css/parse-css-urls.cc
@@ -1,6 +1,8 @@
 #include "cpp/htmlparser/css/parse-css-urls.h"
 
 #include <memory>
+#include <string>
+#include <utility>
 
 #include "absl/algorithm/container.h"
 #include "absl/memory/memory.h"
diff --git a/validator/cpp/htmlparser/css/parse-css-urls_test.cc b/validator/cpp/htmlparser/css/parse-css-urls_test.cc
index 844412770512..3198d3c0d044 100644
--- a/validator/cpp/htmlparser/css/parse-css-urls_test.cc
+++ b/validator/cpp/htmlparser/css/parse-css-urls_test.cc
@@ -1,13 +1,14 @@
 #include "cpp/htmlparser/css/parse-css-urls.h"
 
 #include <ostream>
+#include <string>
+#include <vector>
 
 #include <gmock/gmock.h>
 #include "gtest/gtest.h"
 #include "absl/strings/str_cat.h"
 #include "cpp/htmlparser/strings.h"
 
-using testing::Eq;
 using testing::Pointwise;
 
 namespace htmlparser::css::url {
diff --git a/validator/cpp/htmlparser/css/parse-css.cc b/validator/cpp/htmlparser/css/parse-css.cc
index 4df12b588e33..86c96098da2d 100644
--- a/validator/cpp/htmlparser/css/parse-css.cc
+++ b/validator/cpp/htmlparser/css/parse-css.cc
@@ -2,6 +2,11 @@
 
 #include <deque>
 #include <memory>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
 
 #include "absl/algorithm/container.h"
 #include "absl/memory/memory.h"
diff --git a/validator/cpp/htmlparser/css/parse-css_test.cc b/validator/cpp/htmlparser/css/parse-css_test.cc
index 850a67f4ed76..3226c0f9d936 100644
--- a/validator/cpp/htmlparser/css/parse-css_test.cc
+++ b/validator/cpp/htmlparser/css/parse-css_test.cc
@@ -1,6 +1,10 @@
 #include "cpp/htmlparser/css/parse-css.h"
 
+#include <algorithm>
 #include <memory>
+#include <string>
+#include <string_view>
+#include <utility>
 #include <vector>
 
 #include <gmock/gmock.h>
diff --git a/validator/cpp/htmlparser/data/CaseFolding.txt b/validator/cpp/htmlparser/data/CaseFolding.txt
index 65aa0fcd6b32..69c5c64b4c6a 100644
--- a/validator/cpp/htmlparser/data/CaseFolding.txt
+++ b/validator/cpp/htmlparser/data/CaseFolding.txt
@@ -1,6 +1,6 @@
-# CaseFolding-15.0.0.txt
-# Date: 2022-02-02, 23:35:35 GMT
-# © 2022 Unicode®, Inc.
+# CaseFolding-15.1.0.txt
+# Date: 2023-05-12, 21:53:10 GMT
+# © 2023 Unicode®, Inc.
 # Unicode and the Unicode Logo are registered trademarks of Unicode, Inc. in the U.S. and other countries.
 # For terms of use, see https://www.unicode.org/terms_of_use.html
 #
@@ -929,6 +929,7 @@
 1FCC; S; 1FC3; # GREEK CAPITAL LETTER ETA WITH PROSGEGRAMMENI
 1FD2; F; 03B9 0308 0300; # GREEK SMALL LETTER IOTA WITH DIALYTIKA AND VARIA
 1FD3; F; 03B9 0308 0301; # GREEK SMALL LETTER IOTA WITH DIALYTIKA AND OXIA
+1FD3; S; 0390; # GREEK SMALL LETTER IOTA WITH DIALYTIKA AND OXIA
 1FD6; F; 03B9 0342; # GREEK SMALL LETTER IOTA WITH PERISPOMENI
 1FD7; F; 03B9 0308 0342; # GREEK SMALL LETTER IOTA WITH DIALYTIKA AND PERISPOMENI
 1FD8; C; 1FD0; # GREEK CAPITAL LETTER IOTA WITH VRACHY
@@ -937,6 +938,7 @@
 1FDB; C; 1F77; # GREEK CAPITAL LETTER IOTA WITH OXIA
 1FE2; F; 03C5 0308 0300; # GREEK SMALL LETTER UPSILON WITH DIALYTIKA AND VARIA
 1FE3; F; 03C5 0308 0301; # GREEK SMALL LETTER UPSILON WITH DIALYTIKA AND OXIA
+1FE3; S; 03B0; # GREEK SMALL LETTER UPSILON WITH DIALYTIKA AND OXIA
 1FE4; F; 03C1 0313; # GREEK SMALL LETTER RHO WITH PSILI
 1FE6; F; 03C5 0342; # GREEK SMALL LETTER UPSILON WITH PERISPOMENI
 1FE7; F; 03C5 0308 0342; # GREEK SMALL LETTER UPSILON WITH DIALYTIKA AND PERISPOMENI
@@ -1328,6 +1330,7 @@ FB02; F; 0066 006C; # LATIN SMALL LIGATURE FL
 FB03; F; 0066 0066 0069; # LATIN SMALL LIGATURE FFI
 FB04; F; 0066 0066 006C; # LATIN SMALL LIGATURE FFL
 FB05; F; 0073 0074; # LATIN SMALL LIGATURE LONG S T
+FB05; S; FB06; # LATIN SMALL LIGATURE LONG S T
 FB06; F; 0073 0074; # LATIN SMALL LIGATURE ST
 FB13; F; 0574 0576; # ARMENIAN SMALL LIGATURE MEN NOW
 FB14; F; 0574 0565; # ARMENIAN SMALL LIGATURE MEN ECH
diff --git a/validator/cpp/htmlparser/doctype.cc b/validator/cpp/htmlparser/doctype.cc
index 13cb08531323..1cb49ccb3054 100644
--- a/validator/cpp/htmlparser/doctype.cc
+++ b/validator/cpp/htmlparser/doctype.cc
@@ -1,6 +1,8 @@
 #include "cpp/htmlparser/doctype.h"
 
 #include <sstream>
+#include <string>
+#include <string_view>
 
 #include "cpp/htmlparser/strings.h"
 
diff --git a/validator/cpp/htmlparser/document.cc b/validator/cpp/htmlparser/document.cc
index 4f54b2713f38..337dc73ece53 100644
--- a/validator/cpp/htmlparser/document.cc
+++ b/validator/cpp/htmlparser/document.cc
@@ -1,6 +1,10 @@
-#include "absl/flags/flag.h"
 #include "cpp/htmlparser/document.h"
 
+#include <algorithm>
+#include <iterator>
+
+#include "absl/flags/flag.h"
+
 ABSL_FLAG(std::size_t, htmlparser_nodes_allocator_block_size,
           256 << 10 /* 256k */,
           "Allocator block size for html nodes.");
diff --git a/validator/cpp/htmlparser/error.cc b/validator/cpp/htmlparser/error.cc
index 36f8f31355c8..1b8491d2d84a 100644
--- a/validator/cpp/htmlparser/error.cc
+++ b/validator/cpp/htmlparser/error.cc
@@ -1,5 +1,8 @@
 #include "cpp/htmlparser/error.h"
 
+#include <optional>
+#include <string>
+
 namespace htmlparser {
 
 std::optional<Error> error(const std::string& error_msg) {
diff --git a/validator/cpp/htmlparser/fileutil.cc b/validator/cpp/htmlparser/fileutil.cc
index 58b5834bf9b1..ff21f1b6cec2 100644
--- a/validator/cpp/htmlparser/fileutil.cc
+++ b/validator/cpp/htmlparser/fileutil.cc
@@ -3,10 +3,15 @@
 #include <glob.h>
 
 #include <algorithm>
+#include <cctype>
 #include <cstring>
 #include <fstream>
 #include <iostream>
 #include <sstream>
+#include <string>
+#include <string_view>
+#include <variant>
+#include <vector>
 
 #include "cpp/htmlparser/defer.h"
 #include "cpp/htmlparser/strings.h"
diff --git a/validator/cpp/htmlparser/fileutil_test.cc b/validator/cpp/htmlparser/fileutil_test.cc
index 5d4b4f807839..2ac532717d0d 100644
--- a/validator/cpp/htmlparser/fileutil_test.cc
+++ b/validator/cpp/htmlparser/fileutil_test.cc
@@ -1,5 +1,8 @@
 #include "cpp/htmlparser/fileutil.h"
 
+#include <sstream>
+#include <string>
+#include <string_view>
 #include <vector>
 
 #include "gtest/gtest.h"
diff --git a/validator/cpp/htmlparser/foreign.cc b/validator/cpp/htmlparser/foreign.cc
index bd425bdd9003..a1d8e9f63ac8 100644
--- a/validator/cpp/htmlparser/foreign.cc
+++ b/validator/cpp/htmlparser/foreign.cc
@@ -1,6 +1,10 @@
 #include "cpp/htmlparser/foreign.h"
 
 #include <algorithm>
+#include <array>
+#include <string>
+#include <string_view>
+#include <vector>
 
 #include "cpp/htmlparser/comparators.h"
 #include "cpp/htmlparser/strings.h"
diff --git a/validator/cpp/htmlparser/grammar/tablebuilder.cc b/validator/cpp/htmlparser/grammar/tablebuilder.cc
index 69368df66893..019b45b6b716 100644
--- a/validator/cpp/htmlparser/grammar/tablebuilder.cc
+++ b/validator/cpp/htmlparser/grammar/tablebuilder.cc
@@ -6,6 +6,13 @@
 #include <fstream>
 #include <iostream>
 #include <iterator>
+#include <map>
+#include <optional>
+#include <set>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <vector>
 
 #include "absl/strings/match.h"
 #include "cpp/htmlparser/defer.h"
diff --git a/validator/cpp/htmlparser/htmldataset_test.cc b/validator/cpp/htmlparser/htmldataset_test.cc
index 443238b623e1..80fa4e69ca90 100644
--- a/validator/cpp/htmlparser/htmldataset_test.cc
+++ b/validator/cpp/htmlparser/htmldataset_test.cc
@@ -1,15 +1,17 @@
 // Runs webkit html5 test datasets and validates parser.
 
+#include <algorithm>
 #include <array>
 #include <fstream>
 #include <iostream>
+#include <memory>
+#include <optional>
 #include <sstream>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "gtest/gtest.h"
-#include "absl/flags/flag.h"
 #include "cpp/htmlparser/atomutil.h"
 #include "cpp/htmlparser/defer.h"
 #include "cpp/htmlparser/fileutil.h"
@@ -22,7 +24,8 @@
 
 ABSL_FLAG(std::string, test_srcdir, "", "Testdata directory");
 
-using namespace htmlparser;
+
+namespace htmlparser {
 
 // Represents a single test case.
 struct TestCaseData {
@@ -113,7 +116,7 @@ TestCaseData ReadParseTest(std::ifstream* fd) {
     line = ReadUntil(fd, "\n");
     std::string trimmed(line);
     Strings::Trim(&trimmed, "| \n");
-    if (trimmed.size() > 0) {
+    if (!trimmed.empty()) {
       if (line.front() == '|' && trimmed.front() == '"') {
         in_quote = true;
       }
@@ -191,7 +194,7 @@ std::optional<Error> DumpLevel(Node* node, std::stringbuf* buffer,
         std::string v = attr.value;
         buffer->sputc('\n');
         DumpIndent(buffer, level);
-        if (ns != "") {
+        if (!ns.empty()) {
           buffer->sputn(ns.c_str(), ns.size());
           buffer->sputc(' ');
           buffer->sputn(k.c_str(), k.size());
@@ -305,9 +308,7 @@ TEST(HTMLDatasetTest, WebkitData) {
   };
   int num_test_cases = 0;
   for (auto pattern : htmlparser::testing::kTestDataDirs) {
-    std::string full_path =
-        absl::GetFlag(FLAGS_test_srcdir) +
-        pattern.data();
+    std::string full_path = ::testing::SrcDir() + pattern.data();
     std::vector<std::string> filenames;
     EXPECT_TRUE(FileUtil::Glob(full_path, &filenames))
         << "Error opening files: " << pattern;
@@ -388,4 +389,6 @@ TEST(HTMLDatasetTest, WebkitData) {
   // Hardcoded, whenever dataset changes. Ensures no new tests are added, or
   // old tests mistakenly removed.
   EXPECT_EQ(1484, num_test_cases);
-};
+}
+
+}  // namespace htmlparser
diff --git a/validator/cpp/htmlparser/json/json.cc b/validator/cpp/htmlparser/json/json.cc
index 6dec3e7bc28a..b49cb4ae3400 100644
--- a/validator/cpp/htmlparser/json/json.cc
+++ b/validator/cpp/htmlparser/json/json.cc
@@ -1,6 +1,10 @@
 #include "cpp/htmlparser/json/json.h"
 
+#include <memory>
 #include <stack>
+#include <string>
+#include <string_view>
+#include <utility>
 
 #include "absl/strings/numbers.h"
 #include "cpp/htmlparser/logging.h"
diff --git a/validator/cpp/htmlparser/json/json_test.cc b/validator/cpp/htmlparser/json/json_test.cc
index b9e688e19654..082dacdf2796 100644
--- a/validator/cpp/htmlparser/json/json_test.cc
+++ b/validator/cpp/htmlparser/json/json_test.cc
@@ -1,5 +1,7 @@
 #include "cpp/htmlparser/json/json.h"
 
+#include <string>
+
 #include <gmock/gmock.h>
 #include "gtest/gtest.h"
 #include "cpp/htmlparser/json/types.h"
diff --git a/validator/cpp/htmlparser/json/types.cc b/validator/cpp/htmlparser/json/types.cc
index 9500a17df7e6..7ca54567994b 100644
--- a/validator/cpp/htmlparser/json/types.cc
+++ b/validator/cpp/htmlparser/json/types.cc
@@ -1,6 +1,10 @@
 #include "cpp/htmlparser/json/types.h"
 
 #include <array>
+#include <sstream>
+#include <string>
+#include <string_view>
+#include <variant>
 
 namespace htmlparser::json {
 
diff --git a/validator/cpp/htmlparser/json/types_test.cc b/validator/cpp/htmlparser/json/types_test.cc
index 9a9862943bc8..0e265612fed4 100644
--- a/validator/cpp/htmlparser/json/types_test.cc
+++ b/validator/cpp/htmlparser/json/types_test.cc
@@ -1,7 +1,11 @@
 #include "cpp/htmlparser/json/types.h"
 
 #include <cmath>
+#include <functional>
+#include <string>
+#include <string_view>
 #include <type_traits>
+#include <utility>
 
 #include "gtest/gtest.h"
 
diff --git a/validator/cpp/htmlparser/node.cc b/validator/cpp/htmlparser/node.cc
index d7441a7a0c5b..8fb8b38b49f5 100644
--- a/validator/cpp/htmlparser/node.cc
+++ b/validator/cpp/htmlparser/node.cc
@@ -2,7 +2,11 @@
 
 #include <algorithm>
 #include <functional>
+#include <optional>
 #include <sstream>
+#include <string>
+#include <string_view>
+#include <vector>
 
 #include "absl/strings/str_join.h"
 #include "absl/strings/string_view.h"
@@ -45,7 +49,7 @@ void Node::DropDuplicateAttributes() {
 }
 
 bool Node::IsSpecialElement() const {
-  if (name_space_ == "" || name_space_ == "html") {
+  if (name_space_.empty() || name_space_ == "html") {
     return std::find(kSpecialElements.begin(),
                      kSpecialElements.end(),
                      atom_) != kSpecialElements.end();
@@ -156,7 +160,7 @@ void Node::ReparentChildrenTo(Node* destination) {
 }
 
 Node* NodeStack::Pop() {
-  if (stack_.size() > 0) {
+  if (!stack_.empty()) {
     Node* node = stack_.back();
     stack_.pop_back();
     return node;
@@ -175,7 +179,7 @@ void NodeStack::Pop(int count) {
 }
 
 Node* NodeStack::Top() {
-  if (stack_.size() > 0) return stack_.at(stack_.size() - 1);
+  if (!stack_.empty()) return stack_.at(stack_.size() - 1);
   return nullptr;
 }
 
@@ -427,7 +431,7 @@ void Node::UpdateChildNodesPositions(Node* relative_node) {
   }
 }
 
-std::string Node::DebugString() {
+std::string Node::DebugString() const {
   std::ostringstream ost;
   switch (node_type_) {
     case NodeType::ELEMENT_NODE:
diff --git a/validator/cpp/htmlparser/node.h b/validator/cpp/htmlparser/node.h
index 31b8c9482ce4..4693936be113 100644
--- a/validator/cpp/htmlparser/node.h
+++ b/validator/cpp/htmlparser/node.h
@@ -129,7 +129,7 @@ class Node {
 
   // Debug/Logging utils.
   // Outputs node debug info.
-  std::string DebugString();
+  std::string DebugString() const;
 
  private:
   void SetManufactured(bool is_manufactured) {
diff --git a/validator/cpp/htmlparser/node_test.cc b/validator/cpp/htmlparser/node_test.cc
index 3bca02f512dd..1ff7a9de8333 100644
--- a/validator/cpp/htmlparser/node_test.cc
+++ b/validator/cpp/htmlparser/node_test.cc
@@ -1,5 +1,8 @@
 #include "cpp/htmlparser/node.h"
 
+#include <memory>
+#include <sstream>
+
 #include "gtest/gtest.h"
 #include "cpp/htmlparser/atom.h"
 #include "cpp/htmlparser/document.h"
@@ -16,7 +19,7 @@ using htmlparser::RenderError;
 using htmlparser::Renderer;
 
 // For operator""s.
-using namespace std::string_literals;
+using namespace std::string_literals;  // NOLINT(build/namespaces)
 
 TEST(NodeTest, BasicStackFunctionality) {
   NodeStack stack;
diff --git a/validator/cpp/htmlparser/parser.cc b/validator/cpp/htmlparser/parser.cc
index 1ddbd303054d..02fc4e8e4a00 100644
--- a/validator/cpp/htmlparser/parser.cc
+++ b/validator/cpp/htmlparser/parser.cc
@@ -1,9 +1,16 @@
 #include <algorithm>
-#include <set>
-#include <tuple>
+#include <functional>
 #ifdef DUMP_NODES
 #include <iostream>  // For DumpDocument
 #endif               // DUMP_NODES
+#include <iterator>
+#include <memory>
+#include <optional>
+#include <set>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
 
 #include "absl/flags/flag.h"
 #include "absl/status/status.h"
@@ -462,7 +469,7 @@ void Parser::AddFormattingElement() {
     Node* node = active_formatting_elements_stack_.at(i);
     if (node->node_type_ == NodeType::SCOPE_MARKER_NODE) break;
     if (node->node_type_ != NodeType::ELEMENT_NODE) continue;
-    if (node->name_space_ != "") continue;
+    if (!node->name_space_.empty()) continue;
     if (node->atom_ != tag_atom) continue;
     if (node->attributes_.size() != token_.attributes.size()) continue;
 
@@ -1703,7 +1710,7 @@ bool Parser::InBodyIM() {  // NOLINT
       break;
     }
     case TokenType::ERROR_TOKEN: {
-      if (template_stack_.size() > 0) {
+      if (!template_stack_.empty()) {
         insertion_mode_ = std::bind(&Parser::InTemplateIM, this);
         return false;
       } else {
diff --git a/validator/cpp/htmlparser/parser_test.cc b/validator/cpp/htmlparser/parser_test.cc
index 4a5a74de57ed..360bbf335a3c 100644
--- a/validator/cpp/htmlparser/parser_test.cc
+++ b/validator/cpp/htmlparser/parser_test.cc
@@ -1,5 +1,8 @@
 #include "cpp/htmlparser/parser.h"
 
+#include <sstream>
+#include <string>
+
 #include "gtest/gtest.h"
 #include "absl/flags/declare.h"
 #include "absl/flags/flag.h"
diff --git a/validator/cpp/htmlparser/renderer_test.cc b/validator/cpp/htmlparser/renderer_test.cc
index 1c37bc55a058..a502ef11b38b 100644
--- a/validator/cpp/htmlparser/renderer_test.cc
+++ b/validator/cpp/htmlparser/renderer_test.cc
@@ -1,11 +1,14 @@
 #include "cpp/htmlparser/renderer.h"
 
 #include <sstream>
+#include <string>
+#include <string_view>
+#include <vector>
 
 #include "gtest/gtest.h"
 #include "cpp/htmlparser/parser.h"
 
-using namespace std::string_literals;
+using namespace std::string_literals;  // NOLINT(build/namespaces)
 
 namespace htmlparser {
 
@@ -167,4 +170,4 @@ TEST(RendererTest, NullCharsTest) {
     htmlparser::CheckParseRenderOutput(
         html_sources.at(i), rendered_outputs.at(i));
   }
-};
+}
diff --git a/validator/cpp/htmlparser/strings.cc b/validator/cpp/htmlparser/strings.cc
index 999ab6622912..4e1027cfb253 100644
--- a/validator/cpp/htmlparser/strings.cc
+++ b/validator/cpp/htmlparser/strings.cc
@@ -3,8 +3,13 @@
 #include <algorithm>
 #include <array>
 #include <functional>
+#include <ios>  // For std::hex
+#include <optional>
 #include <sstream>
+#include <string>
 #include <tuple>
+#include <utility>
+
 #include "cpp/htmlparser/casetable.h"
 #include "cpp/htmlparser/entity.h"
 #include "cpp/htmlparser/whitespacetable.h"
@@ -15,7 +20,7 @@ namespace htmlparser {
 // assumed Windows-1252 encoding.
 // https://html.spec.whatwg.org/multipage/syntax.html#consume-a-character-reference
 constexpr std::array<char32_t, 32> kReplacementTable{
-    L'\u20AC', // First entry is what 0x80 should be replaced with.
+    L'\u20AC',  // First entry is what 0x80 should be replaced with.
     L'\u0081',
     L'\u201A',
     L'\u0192',
@@ -46,7 +51,7 @@ constexpr std::array<char32_t, 32> kReplacementTable{
     L'\u0153',
     L'\u009D',
     L'\u017E',
-    L'\u0178', // Last entry is 0x9F.
+    L'\u0178',  // Last entry is 0x9F.
     // 0x00->L'\uFFFD' is handled programmatically.
     // 0x0D->L'\u000D' is a no-op.
 };
@@ -645,7 +650,7 @@ bool Strings::EqualFold(std::string_view l, std::string_view r) {
         if ((l_char | 0x20) != (r_char | 0x20)) {
           return false;
         }
-      } else if (l_char != r_char) { // Compare other ascii character as-is.
+      } else if (l_char != r_char) {  // Compare other ascii character as-is.
         return false;
       }
 
@@ -846,13 +851,13 @@ std::pair<int, int> UnescapeEntity(std::string* b, int dst, int src,
     i++;
     // Lower-cased characters are more common in entities, so we check for
     // them first.
-   if (Strings::IsCharAlphabet(c) || Strings::IsDigit(c)) {
+    if (Strings::IsCharAlphabet(c) || Strings::IsDigit(c)) {
      continue;
-   }
-   if (c != ';') {
-     i--;
-   }
-   break;
+    }
+    if (c != ';') {
+      i--;
+    }
+    break;
   }
 
   std::string entityName = s.substr(1, i - 1);
@@ -900,7 +905,6 @@ std::pair<int, int> UnescapeEntity(std::string* b, int dst, int src,
 
 void CaseTransformInternal(bool to_upper, std::string* s) {
   for (std::size_t i = 0; i < s->size(); ++i) {
-
     uint8_t code_point = s->at(i) & 0xff;
 
     // ASCII characters first.
diff --git a/validator/cpp/htmlparser/strings_test.cc b/validator/cpp/htmlparser/strings_test.cc
index 2ae273c41c4b..763a6ff22819 100644
--- a/validator/cpp/htmlparser/strings_test.cc
+++ b/validator/cpp/htmlparser/strings_test.cc
@@ -1,10 +1,13 @@
 #include "cpp/htmlparser/strings.h"
 
+#include <sstream>
 #include <string>
+#include <string_view>
+#include <vector>
 
 #include "gtest/gtest.h"
 
-using namespace std::string_literals;
+using namespace std::string_literals;  // NOLINT(build/namespaces)
 
 TEST(StringsTest, SplitStringAtTest) {
   auto columns = htmlparser::Strings::SplitStringAt("a|b|c", '|');
@@ -410,7 +413,7 @@ TEST(StringsTest, ReplaceTest) {
   htmlparser::Strings::ReplaceAny(&whitespace_and_null2,
                                   htmlparser::Strings::kNullChar,
                                   htmlparser::Strings::kNullReplacementChar);
-  EXPECT_EQ(whitespace_and_null2, "amaltas is ��good �boy");
+  EXPECT_EQ(whitespace_and_null2, "amaltas is ��good �boy");  // NOLINT
 
   std::string many_whitespaces = "  a   m  a lta s  ";
   htmlparser::Strings::RemoveExtraSpaceChars(&many_whitespaces);
diff --git a/validator/cpp/htmlparser/token.cc b/validator/cpp/htmlparser/token.cc
index 5ae0fdd66ed4..fa60af347fc2 100644
--- a/validator/cpp/htmlparser/token.cc
+++ b/validator/cpp/htmlparser/token.cc
@@ -1,5 +1,7 @@
 #include "cpp/htmlparser/token.h"
 
+#include <string>
+
 #include "cpp/htmlparser/strings.h"
 
 namespace htmlparser {
diff --git a/validator/cpp/htmlparser/tokenizer.cc b/validator/cpp/htmlparser/tokenizer.cc
index 49483ac3f6b2..021322556357 100644
--- a/validator/cpp/htmlparser/tokenizer.cc
+++ b/validator/cpp/htmlparser/tokenizer.cc
@@ -1,5 +1,13 @@
 #include "cpp/htmlparser/tokenizer.h"
 
+#include <algorithm>
+#include <optional>
+#include <string>
+#include <string_view>
+#include <tuple>
+#include <utility>
+#include <vector>
+
 #include "absl/flags/flag.h"
 #include "cpp/htmlparser/atom.h"
 #include "cpp/htmlparser/atomutil.h"
@@ -681,6 +689,7 @@ void Tokenizer::ReadTagAttributeKey(bool template_mode) {
   // templates. See: https://amp.dev/documentation/components/amp-mustache/
   bool mustache_inside_section_block = false;
   std::string mustache_section_name = "";
+  bool is_at_attribute_key_start = true;
 
   while (!eof_) {
     char c = ReadByte();
@@ -744,12 +753,21 @@ void Tokenizer::ReadTagAttributeKey(bool template_mode) {
         return;
       }
       case '=':
+        if (is_at_attribute_key_start) {
+          // An unexpected equals sign at the start of the attribute name should
+          // be treated as part of the name. See §13.2.5.32 "Before attribute
+          // name state" in the HTML Living Standard from 2024-02-22 at
+          // https://html.spec.whatwg.org/multipage/parsing.html#before-attribute-name-state.
+          break;
+        }
+        [[fallthrough]];
       case '>': {
         UnreadByte();
         std::get<0>(pending_attribute_).end = raw_.end;
         return;
       }
     }
+    is_at_attribute_key_start = false;
   }
 }
 
@@ -838,7 +856,7 @@ TokenType Tokenizer::Next(bool template_mode) {
     return token_type_;
   }
 
-  if (raw_tag_ != "") {
+  if (!raw_tag_.empty()) {
     if (raw_tag_ == "plaintext") {
       // Read everything up to EOF.
       while (!eof_) {
diff --git a/validator/cpp/htmlparser/tokenizer_test.cc b/validator/cpp/htmlparser/tokenizer_test.cc
index 8c5c9a119fea..b35b92e4c0e1 100644
--- a/validator/cpp/htmlparser/tokenizer_test.cc
+++ b/validator/cpp/htmlparser/tokenizer_test.cc
@@ -1,5 +1,9 @@
 #include "cpp/htmlparser/tokenizer.h"
 
+#include <string>
+#include <string_view>
+#include <vector>
+
 #include "gtest/gtest.h"
 #include "cpp/htmlparser/token.h"
 
@@ -229,6 +233,45 @@ TEST(TokenizerTest, BasicTokenizationOfADocument) {
   // their respective test cases.
 }
 
+// Tests that an unexpected equals sign ("="") at the start of an attribute name
+// is treated as part of the attribute name. See §13.2.5.32 "Before attribute
+// name state" in the HTML Living Standard from 2024-02-22 at
+// https://html.spec.whatwg.org/multipage/parsing.html#before-attribute-name-state.
+TEST(TokenizerTest, UnexpectedEqualsSignAtStartOfAttributeName) {
+  // Attribute name is prefixed with "=" and also has a value.
+  htmlparser::Tokenizer t1("<div =a=\"b\" />");
+  t1.Next();
+  htmlparser::Token token1 = t1.token();
+  EXPECT_EQ(token1.token_type, htmlparser::TokenType::SELF_CLOSING_TAG_TOKEN);
+  EXPECT_EQ(token1.attributes.size(), 1);
+  EXPECT_EQ(token1.attributes[0].key, "=a");
+  EXPECT_EQ(token1.attributes[0].value, "b");
+  EXPECT_EQ(t1.Next(), htmlparser::TokenType::ERROR_TOKEN);
+  EXPECT_TRUE(t1.IsEOF());
+
+  // Attribute name is prefixed with "=" without value.
+  htmlparser::Tokenizer t2("<div =a />");
+  t2.Next();
+  htmlparser::Token token2 = t2.token();
+  EXPECT_EQ(token2.token_type, htmlparser::TokenType::SELF_CLOSING_TAG_TOKEN);
+  EXPECT_EQ(token2.attributes.size(), 1);
+  EXPECT_EQ(token2.attributes[0].key, "=a");
+  EXPECT_EQ(token2.attributes[0].value, "");
+  EXPECT_EQ(t2.Next(), htmlparser::TokenType::ERROR_TOKEN);
+  EXPECT_TRUE(t2.IsEOF());
+
+  // Attribute name is "=" without value.
+  htmlparser::Tokenizer t3("<div = />");
+  t3.Next();
+  htmlparser::Token token3 = t3.token();
+  EXPECT_EQ(token3.token_type, htmlparser::TokenType::SELF_CLOSING_TAG_TOKEN);
+  EXPECT_EQ(token3.attributes.size(), 1);
+  EXPECT_EQ(token3.attributes[0].key, "=");
+  EXPECT_EQ(token3.attributes[0].value, "");
+  EXPECT_EQ(t3.Next(), htmlparser::TokenType::ERROR_TOKEN);
+  EXPECT_TRUE(t3.IsEOF());
+}
+
 TEST(TokenizerTest, TestMustangTemplateCase) {
   std::string_view template_html = R"HTML(<html>
 <head></head>
diff --git a/validator/cpp/htmlparser/url.cc b/validator/cpp/htmlparser/url.cc
index 98c2ad8d01d8..98cdad639169 100644
--- a/validator/cpp/htmlparser/url.cc
+++ b/validator/cpp/htmlparser/url.cc
@@ -1,5 +1,8 @@
 #include "cpp/htmlparser/url.h"
 
+#include <string>
+#include <string_view>
+
 #include "cpp/htmlparser/strings.h"
 
 namespace htmlparser {
diff --git a/validator/cpp/htmlparser/url_test.cc b/validator/cpp/htmlparser/url_test.cc
index ba6e7e0df335..12860f64351b 100644
--- a/validator/cpp/htmlparser/url_test.cc
+++ b/validator/cpp/htmlparser/url_test.cc
@@ -1,5 +1,7 @@
 #include "cpp/htmlparser/url.h"
 
+#include <string>
+
 #include "gtest/gtest.h"
 
 namespace htmlparser {
diff --git a/validator/cpp/htmlparser/validators/ipaddress_test.cc b/validator/cpp/htmlparser/validators/ipaddress_test.cc
index fc3e9584ab02..8e0a0041f344 100644
--- a/validator/cpp/htmlparser/validators/ipaddress_test.cc
+++ b/validator/cpp/htmlparser/validators/ipaddress_test.cc
@@ -1,4 +1,8 @@
 #include "cpp/htmlparser/validators/ipaddress.h"
+
+#include <string_view>
+#include <utility>
+
 #include "gtest/gtest.h"
 
 namespace htmlparser::ipaddress {
diff --git a/validator/cpp/htmlparser/validators/json_test.cc b/validator/cpp/htmlparser/validators/json_test.cc
index 5b9f37adc04d..0c01b9c706cc 100644
--- a/validator/cpp/htmlparser/validators/json_test.cc
+++ b/validator/cpp/htmlparser/validators/json_test.cc
@@ -16,6 +16,8 @@
 
 #include "cpp/htmlparser/validators/json.h"
 
+#include <string_view>
+#include <utility>
 #include <vector>
 
 #include <gmock/gmock.h>
diff --git a/validator/cpp/htmlparser/validators/supported_media_query_test.cc b/validator/cpp/htmlparser/validators/supported_media_query_test.cc
index 26d0b4fb044f..25ed64ea8712 100644
--- a/validator/cpp/htmlparser/validators/supported_media_query_test.cc
+++ b/validator/cpp/htmlparser/validators/supported_media_query_test.cc
@@ -1,5 +1,8 @@
 #include "cpp/htmlparser/validators/supported_media_query.h"
 
+#include <string_view>
+#include <utility>
+
 #include "gtest/gtest.h"
 
 namespace htmlparser::css {