Page Regions
Page header

<header> element, which can be used to define such a region.
View a complete code example for all regions combined.
Page footer

<footer> element, which can be used to define such a region.
Navigation

<nav> element can be used to identify a navigation menu. A web page can have any number of navigation menus. Use labels to identify each navigation menu.
The Menus tutorial provides more details on creating menus.
Main content

<main> element to identify the main content region of a web page or application.
Complementary content

<aside> element to identify regions that support the main content, yet are separate and meaningful sections on their own; For example, a side note explaining or annotating the main content.
Responsive design
Components may be collapsed or even hidden on smaller screens, but components that show should appear in the same order for a particular view (set size and orientation). If possible, page structure should be consistent across different screen sizes and orientations, though not a specific WCAG requirement.
Page regions in HTML4 using WAI-ARIA
If HTML5 cannot be used or if an HTML4 page is retrofitted to improve accessibility, add WAI-ARIA code to div elements that function as their HTML5 counterparts, for example:
Explore other WAI-ARIA resources:
- WAI-ARIA Overview
- ARIA in HTML web standard