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).
Authors MUST NOT include more than one main element in a document.
Note: Authors are advised to use ARIA role="main" attribute on the main element until user agents implement the required role mapping.
in AX_ARIA_05:
role=main
should only appear on significant elements.and in W3