SEO and Valid HTML: How Critical Are W3C Standards?

Woman screaming in terror at the Google logo

If I made a list of requests from new SEO hires, “Fix these HTML errors from the W3C validation tool” would be in the top 5. Thankfully, John Mueller took time in the latest Google Webmaster Central hangout to address the ranking importance (and intended meaning) of “valid HTML” in Search Engine Optimization. He helpfully described the SEO situations well-written HTML avoids, each of which has its own testing tool from Google.