HTML 5 Programming and Web development/HTML 5 Doctype

The HTML 5 Document Type Definition (Doctype) is used to identify the type of markup document. conventionally doctypes are written like this Where in this case the root-element would be HTML.FPI stands for formal public identifier. However in HTML 5 the Doctype is just written

Example of doctype in HTML 5
The doctype must always be at the top of the document.

Document without doctype
Documents without doctype would work in most browsers ,but would not be classified as a valid document.(see Validation).