document.registerElement() rejects a valid unregistered type with U+212A.

third_party/WebKit/Source/core/html/custom/V0CustomElementRegistry.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 30 matching lines @@
 #include "core/html/custom/V0CustomElementRegistrationContext.h"
 
 namespace blink {
 
 V0CustomElementDefinition* V0CustomElementRegistry::RegisterElement(
     Document* document,
     V0CustomElementConstructorBuilder* constructor_builder,
     const AtomicString& user_supplied_name,
     V0CustomElement::NameSet valid_names,
     ExceptionState& exception_state) {
-  AtomicString type = user_supplied_name.DeprecatedLower();
+  AtomicString type = user_supplied_name.LowerASCII();
 
   if (!constructor_builder->IsFeatureAllowed()) {
     V0CustomElementException::ThrowException(
         V0CustomElementException::kCannotRegisterFromExtension, type,
         exception_state);
     return nullptr;
   }
 
   if (!V0CustomElement::IsValidName(type, valid_names)) {
     V0CustomElementException::ThrowException(
@@ skipping 81 matching lines @@
 bool V0CustomElementRegistry::V1NameIsDefined(const AtomicString& name) const {
   return v1_.Get() && v1_->NameIsDefined(name);
 }
 
 DEFINE_TRACE(V0CustomElementRegistry) {
   visitor->Trace(definitions_);
   visitor->Trace(v1_);
 }
 
 }  // namespace blink