What is the ? Is it necessary to use in HTML5 ?

Question :

What is the ? Is it necessary to use in HTML5 ?

The is an instruction to the web browser about what version of HTML the page is written in. AND The tag does not have an end tag and It is not case sensitive. The declaration must be the very first thing in HTML5 document, before the tag. As In HTML 4.01, all declarations require a reference to a Document Type Definition (DTD), because HTML 4.01 was based on Standard Generalized Markup Language (SGML). WHERE AS HTML5 is not based on SGML, and therefore does not require a reference to a Document Type Definition (DTD).