The test incorrectly fails HTML with lang="en-US" when it should be accepted as valid. en-US is a proper language tag per HTML specifications, indicating English as used in the United States.
The error message specifically states “Don’t forget the lang attribute” when the attribute is clearly present. Either the test should accept all valid language codes (including regional variants like en-US) or the instructions should specifically state to use only lang="en" if that’s the expected answer.
