A Document Type Declaration, or DOCTYPE, is an instruction that associates a particular SGML or XML document (for example, a webpage) with a Document Type Definition (DTD) (for example, the formal definition of a particular version of HTML). In the serialized form of the document, it manifests as a short string of markup that conforms to a particular syntax.
The HTML layout engines in modern web browsers perform DOCTYPE "sniffing" or "switching", wherein the DOCTYPE in a document served as text/html determines a layout mode, such as "quirks mode" or "standards mode". The text/html serialization of HTML5, which is not SGML-based, uses the DOCTYPE only for mode selection. Since web browsers are implemented with special-purpose HTML parsers, rather than general-purpose DTD-based parsers, they don't use DTDs and will never access them even if a URL is provided. The DOCTYPE is retained in HTML5 as a "mostly useless, but required" header only to trigger "standards mode" in common browsers.
Famous quotes containing the words document, type and/or declaration:
“... research is never completed ... Around the corner lurks another possibility of interview, another book to read, a courthouse to explore, a document to verify.”
—Catherine Drinker Bowen (1897–1973)
“We have two kinds of “conference.” One is that to which the office boy refers when he tells the applicant for a job that Mr. Blevitch is “in conference.” This means that Mr. Blevitch is in good health and reading the paper, but otherwise unoccupied. The other type of “conference” is bona fide in so far as it implies that three or four men are talking together in one room, and don’t want to be disturbed.”
—Robert Benchley (1889–1945)
“Let us stun and astonish the intruding rabble of men and books and institutions by a simple declaration of the divine fact. Bid the invaders take the shoes from off their feet, for God is here within.”
—Ralph Waldo Emerson (1803–1882)