HTML5 means different things to different people. You could argue that HTML5 only includes features that are defined in the W3C HTML5 specification. Or you could argue that it includes every specification, draft or experimental feature that is added to browsers in the last couple of years. We decided to take the middle ground and split the test into three parts: the official HTML5 specification, specifications that are related to HTML5 and some experimental new features that are extensions of HTML5.
Many of the related specifications were at one time part of HTML5. During the development of the specification they were moved to separate specifications.