A doctype declaration refers to the rules for the markup language, so that the browsers render the content correctly.
An HTML document with a doctype of HTML 4.01 Transitional:
HTML Different Doctypes
The doctype declaration is not an HTML tag; it is an instruction to the web browser about what version of the markup language the page is written in.
The doctype declaration refers to a Document Type Definition (DTD). The DTD specifies the rules for the markup language, so that the browsers render the content correctly.
The doctype declaration should be the very first thing in an HTML document, before the <html> tag.
Tip: Always add a doctype to your pages. This helps the browsers to render the page correctly!
HTML 4.01 Strict
This DTD contains all HTML elements and attributes, but does NOT INCLUDE presentational or deprecated elements (like font and center). Framesets are not allowed:
HTML 4.01 Transitional
This DTD contains all HTML elements and attributes, INCLUDING presentational and deprecated elements (like font). Framesets are not allowed:
HTML 4.01 Frameset
This DTD is equal to HTML 4.01 Transitional, but allows the use of frameset content:
Tips and Notes:
Use W3C’s Validator to check that you have written a valid HTML / XHTML document!
HTML DOCTYPE Element
|<!DOCTYPE>||Defines the document type. This declaration goes before the <html> start tag|
You can use several tools to validate your documents. Tools you have at your disposal include the following:
✦ The online W3C HTML validation tool, found at http://validator.w3.org/.
✦ Validation utilities built in to Web development tools such as Adobe’sDreamweaver.