HTML <!DOCTYPE> tag is the first statement of HTML document which represents a document type. HTML DOCTYPE declaration is used to instruct web browsers about which version of the HTML document written in. HTML DOCTYPE declaration does not have any end tag and not case-sensitive.
Available Common DOCTYPE Declarations
HTML supports different versions of DOCTYPE declarations. Some common DOCTYPE declarations are as below.
HTML 4.01 Strict
HTML 4.01 Strict allows you to use all HTML tags/elements, attributes but does not support presentational content and framesets.
"-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
HTML 4.01 Transitional
HTML 4.01 Transitional allows you to use all HTML tags/elements, attributes plus support presentational content but does not allow framesets.
"-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
HTML 4.01 Frameset
HTML 4.01 Frameset is same as HTML 4.01 Transitional plus allows framesets.
"-//W3C//DTD HTML 4.01 Frameset//EN" "http://www.w3.org/TR/html4/frameset.dtd">
HTML 5
HTML 5 DOCTYPE declaration is the latest document declaration type and yet NOT a standard type.
