§12.2.4.10 Tag name state seems to be missing a handler for U+000D CARRIAGE RETURN. All other CSS whitespace characters terminate the tag name, and the latest version of every current browser (Android, Chrome, Edge, Firefox, Internet Explorer, iOS, Opera, Safari, Windows Phone, and Yandex) already treats carriage return accordingly: http://jsfiddle.net/fjs6do6z/

Current text:

U+0009 CHARACTER TABULATION (tab)

U+000A LINE FEED (LF)

U+000C FORM FEED (FF)

U+0020 SPACE

Switch to the before attribute name state.