Provide a !DOCTYPE statement
Setting the correct document type allows assistive technologies to know what rules to follow while parsing. This level of formatting removes ambiguity in the parsing process and allows greater coverage across different user agents. To determine the doctype declared on the page, open the page’s source code and look for the doctype at the beginning of the HTML code.
A valid doctype MUST be set for all pages.
HTML Validator (PAG-WEB-002-01-T)
Check the page for the presence of a valid doctype declaration.