Here is John’s tweet:
@robinlmay As long as it can be rendered & SD extracted: validation pretty much doesn’t matter.
— John â.o(â§â-½â¦)o.â (@JohnMu) May 1, 2017
Now, when it comes to structured data, href lang and other forms of markup – that markup should validate for Google to properly pick up on the markup. But for normal web ranking, validation is not necessary to rank well in Google.
Most of the web doesn’t validate anyway and Google still needs to discover and rank most of the web’s content.
Forum discussion at Twitter.