HTML5 was the standard released in 2014, with version 5.1 expected to be released this year.
SEOs are always looking for that extra edge to help their Google rankings, and there have been a few who claimed that switching to HTML5 led to increased rankings in Google. Google had said as far back as 2010 that HTML5 was not any kind of ranking signal, so it is likely other reasons that led to the increased rankings in those cases.