This specification is an extension to the HTML5 specification. It defines an element to be used for the identification of the main content area of a document. All normative content in the HTML5 specification, unless specifically overridden by this specification, is intended to be the basis for this specification.
maincontent element formalises the common practice of identification of the main content section of a document using the
id values such as 'content' and 'main'. It also defines an HTML element that embodies the semantics and function of the WAI-ARIA landmark
This specification describes the conformance criteria for user agents (relevant to implementors) and documents (relevant to authors and authoring tool implementors).
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative. The key words must, must not, required, should, should not, recommended, may, and optional in this specification are to be interpreted as described in [RFC2119].
bodyelement containing no other
sectionelement that is the child of 0 or more
divelements that are children of a
maincontentelement represents the main content section of the
bodyof a document or application. The main content section consists of content that is directly related to or expands upon the central topic of a document or central functionality of an application.
The main content section of a document includes content that is unique to that document and excludes content that is repeated across a set of documents such as site navigation links, copyright information, site logos and banners and search forms (unless the document or applications main function is that of a search form).
User agents that support keyboard navigation of content SHOULD provide a method to move focus to the first interactive element within the
maincontent element. This will provide a simple method for keyboard users to bypass blocks of content such as navigation links. User agents MUST map the
maincontent element to the WAI-ARIA landmark role of
maincontent element is not sectioning content and has no effect on the document outline
In the following example, we see 2 articles about apples (the main topic of a
Web page) the main topic content is identified by the use of the
<!-- other content --> <maincontent> <h1>Apples</h1> <p>The apple is the pomaceous fruit of the apple tree.</p> <article> <h2>Red Delicious</h2> <p>These bright red apples are the most common found in many supermarkets.</p> </article> <article> <h2>Granny Smith</h2> <p>These juicy, green apples make a great filling for apple pies.</p> </article> </maincontent> <!-- other content -->
Here is a graduation programme the main topic content is defined by the use of the
<!DOCTYPE html> <html> <head>
<title>Graduation Ceremony Summer 2022</title> </head> <body> <!-- other content --> <maincontent> <h1>Graduation</h1> <H2>Ceremony</H2> <p>Opening Procession</p> <p>Speech by Valedictorian</p> <p>Speech by Class President</p> <p>Presentation of Diplomas</p> <p>Closing Speech by Headmaster</p> <h2>Graduates</h2>
<ul><li>Molly Carpenter</li> <li>Anastasia Luccio</li> <li>Ebenezar McCoy</li> <li>Karrin Murphy</li> <li>Thomas Raith</li> <li>Susan Rodriguez</li> </ul> </maincontent> <!-- other content --> </body> </html>
From publicly reported studies  of
id values used in HTML content, the use of the strings "content" and "main" are common practice.
 http://triin.net/2006/06/12/CSS#figure-34, http://westciv.typepad.com/dog_or_higher/2005/11/real_world_sema.html, http://dev.opera.com/articles/view/mama-common-attributes/#id