HTML, HTML5 : What does DOCTYPE mean?

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.

Why do I want to use it?

The term DOCTYPE tells the browser which type of HTML is used on a webpage. In turn, the browsers use DOCTYPE to determine how to render a page. Failing to use DOCTYPE or using a wrong DOCTYPE may load your page in Quirks Mode. See example:

 Declaring that the document contains HTML5 Markup

The doctype for HTML5 is very simple. To indicate that your HTML content uses HTML5, simply use:

Doing so will cause even browsers that don’t presently support HTML5 to enter into standards mode, which means that they’ll interpret the long-established parts of HTML in an HTML5-compliant way while ignoring the new features of HTML5 they don’t support.

This is much simpler than the former doctypes, and shorter, making it easier to remember and reducing the amount of bytes that must be downloaded.


Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code class="" title="" data-url=""> <del datetime=""> <em> <i> <q cite=""> <strike> <strong> <pre class="" title="" data-url=""> <span class="" title="" data-url="">