HTML tag

On the HTML document you have often seen that there is a declaration before the tag. HTML tag is used to inform the browser about the version of HTML used in the document. It is called as the document type declaration (DTD).

Technically is not a tag/element, it just an instruction to the browser about the document type. It is a null element which does not contain the closing tag, and must not include any content within it.

Actually, there are many type of HTML e.g. HTML 4.01 Strict, HTML 4.01 Transitional, HTML 4.01 Frameset, XHTML 1.0 Strict, XHTML 1.0 Transitional, XHTML 1.0 Frameset, XHTML 1.1 etc.

The declaration refers Document Type Declaration (DTD) in HTML 4.01; because HTML 4.01 was based on SGML. But HTML 5 is not SGML based language.

DTD defines the rules for the markup languages so that the browsers recognize the content correctly.

The doctype declaration differs between HTML versions. The HTML 5 doctype declaration is given below.

Syntax

Following are some specifications about the HTML

Let's see an example of HTML document with doctype declaration.

Note: It is always a good practice to add a declaration to your HTML documents to enable web browser to recognize that what type of document to expect.

Supporting Browsers

Element	Chrome	IE	Firefox	Opera	Safari
	Yes	Yes	Yes	Yes	Yes

Note: DOCTYPE declaration is not case sensitive.