Use a public text identifier in a DOCTYPE statement |
WAI / WCAG 1.0 Priority 2 checkpoint 3.2
Issue Description The DOCTYPE element is missing or is not valid.
How to fix If the DOCTYPE element is missing, then add one. If it is not valid, then edit and correct it. Check the validity of the DOCTYPE by using the Validator. The DOCTYPE should contain the HTML language version that is used. For example, HTML 4.01 can be based on three different variants (i.e. three DTDs). It is important to include one of the following document type declarations in the documents. The DTDs vary in the elements they support.
To define the DOCTYPE of the page include one of the following just before the HTML tag, at the beginning of the document:

      <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
           "http://www.w3.org/TR/html4/strict.dtd">

      <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
           "http://www.w3.org/TR/html4/loose.dtd">

      <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN"
           "http://www.w3.org/TR/html4/frameset.dtd">

The following DOCTYPE is for XHMTL strict (and similar ones exist for the Transitional and Frameset flavors: see the XHTML 1.0 page [http://www.w3.org/MarkUp/#xhtml1] by W3C):

      <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
        "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

Issue Explanation According to HTML standards, each HTML document requires a Document Type Declaration. The "DOCTYPE" begins the HTML document and tells which version of HTML to expect when processing the document. The DOCTYPE declaration identifies the computer language and version in which the document has been coded. With this information browsers can interpret accessibility features in the document correctly.
This requirement is important for accessibility because assistive technologies may rely on this declaration to determine how to process the document.

When using non-HTML documents (for example when using SMIL or SVG) use the appropriate DOCTYPE declaration for that markup language to ensure that browsers do not attempt to interpret it incorrectly as HTML.