HTML and CSS Reference
Headings, headers, and the outlining algorithm
Heading elements provide an implicit structure for documents. A head-
ing indicates the start of a new section and briefly describes the topic of
the text that follows. The level of a heading (levels 1 through 6 in
HTML ) indicates an implicit hierarchy. This implicit structure is useful
for the automatic generation of a table of contents. Some websites,
such as Wikipedia, generate a table of contents for each page; screen
readers and other accessibility tools use the table of contents to allow
users to navigate the page more easily. HTML5 formalizes this implicit
structure with the outlining algorithm. In this section, you'll learn
about this algorithm as well as how it interacts with the two new head-
ing elements, <header> and <hgroup> .
A <header> element appears near the top of a document, a section, or an
article and usually contains the main heading and often some naviga-
tion and search tools. Here's an example from the BBC website.