This is an archived snapshot of W3C's public bugzilla bug tracker, decommissioned in April 2019. Please see the home page for more details.
The definition of the H# elements has changed substantially, but this isn't noted in Section 3.3.
Can you explain how they changed substantially?
All in all, the definition has been completely re-written and made more stringent, and includes dependencies on other (new) elements (<section>): - In HTML 4 the definition emphasizes "importance" of the heading. This is (and certainly has historically been interpreted as) orthogonal to the "formal" purpose of headings - specifically - identification of content sections. - In HTML 5 the definition ignores the question of "importance" and restricts ("must") use of H1-H6 to section headings. The heading numbers are "ranks" rather than being indications of importance. - The interaction with <section> is also new to HTML5 - and fundamental to the implementation of H1-H6 (not least, because it allows for more than 6 heading levels). - There are additional specifications for headings in the case of <td> and <blockquote> elements. I hope this helps.