Overview

This group presents elements related in their role in sectioning the flow content of the body. They hold in common: little/no specific attributes, little/no direct prose, often being either referenced via an ID or having a singleton relationship to one, being block displayed (not inline). It holds the four sectioning content elements. article, aside, nav and section. Those elements are the root of sub-trees, that the remaining elements of this group are expected to be semantically scoped to, and they are strongly encouraged to contain one heading or equivalent heading group as a first child. The tree created from those elements forms the outline of the page. Its correctness is pivotal to assistive reading technologies, thus accessibility, crawler discovery, search-engine ranking.

section Generic Section

Section partitions the document and the first child should often be a heading of appropriate level. Most elements in this group are close equivalents, but with more semantic specificity. No specific attributes.

article Article Contents

Section with content coherent independently of the rest of the document. Each should be identified by a heading child. When nested within a section, represents an article related to the outer element. Should they be specified, not outwardly applicable: No specific attributes.

main Main

Semantically a section (but does not introduce a new section in the outline) with core content of the document / no para-textual context. No specific attributes, but the global hidden has an important specificity here: a document must have a single main that is not hidden. Must be hierarchically correct i.e. only directly within html or equivalently body, or a div, or a form without accesible name, or an autonomous custom elements, that is an element not registered with a class extending an existing element.

hgroup Heading Group

Heading sub-section with one heading and some paragraphs related to, acting as "subtitles" or para-textual complements to the heading. In the outline acts as a pass-through element to the contained heading. May only contain one h1-6 and any number of p before and/or after. No specific attributes. 

  <hgroup> <h3>Heading within a group.</h3>
    <p>More information sub-title.</p>
  </hgroup>

Heading Elements / Section Headings

Six elements in one: h1, h2, h3, h4, h5, h6. There should be one h1 per document. Then, lower level should form a coherent tree, where there is no level jumped e.g. from h2 to h5. No specific attributes.

Notably the only element encoding a parameter in the tag, in other words, only six HTML tags with a number. Their genesis is from the ealier header, then declined in six levels in the original 1993 set, designed to rely on attributes (3 years before CSS). The ten other from the set, non-deprecated: a, title, p dl, dt, dd, ul, li, menu and address.

address The Contact Address element

Section with contact information for the resource owner. Only represents the nearest ancestor article or body. Must not be a descendant of an address. Must not be ancestor to a header or footer element. Must not be ancestor to any heading. Must not be ancestor to any sectioning. Must contain only the contact information. A common sub-tree is footer containing address and other prose metadata. No specific attributes.
Contact John Doe, 8001, Zürich

aside Aside

Section with content indirectly related to the rest. Must not be a descendant of an address element. Must not be used to wrap main-flow parenthesized text. No specific attributes.