doctype tag

If you don't know what an element is or how you must use it, I recommend you read the "HTML tags and attributes" tutorial that you can find in the HTML tutorials section.

Table of contents

Description

The HTML !DOCTYPE tag is the very first thing that every compliant web document should have. It's purpose is to inform the browser the type of document it's about to process.

In HTML5, the !DOCTYPE declaration remains only for legacy reasons pertaining processing modes in browsers.

The Document Type Declaration (DTD) is unique for each version of HTML and must be written exactly as it is, to be of some use. For this reason, it's better if you just copy and paste the code for the declararion you're about to use.

Below is a list of DTDs for all the versions of HTML (XHTML included), and others like SVG and MathML. But remember that, as of today, there's no need to use any other declaration than the one for HTML5, as this is, by far, the preferred version (unless you're working on a very particular project).

HTML5

<!DOCTYPE html>

XHTML 1.1

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"  "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">

XHTML 1.0

XHTML 1.0 came in three subversions denominated "Strict", "Transitional" and "Frameset". The first two are different in the way they consider valid elements, attributes or syntax, being the "Transitional" version more permissive. The "Frameset" DTD is the same as "Transitional" but with support for frames.

Strict

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

Transitional

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

Frameset

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">

XHTML 1.1 + MathML 2.0 + SVG 1.1

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1 plus MathML 2.0 plus SVG 1.1//EN" "http://www.w3.org/2002/04/xhtml-math-svg/xhtml-math-svg.dtd">

SVG 1.1

SVG 1.1 came in three versions that are different in the complexity of their systax and the availability of resources. The "Basic" and "Tiny" versions were designed specifically for mobile devices.

Full

<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">

Basic

<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1 Basic//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-basic.dtd">

Tiny

<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1 Tiny//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11-tiny.dtd">

SVG 1.0

<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.0//EN" "http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd">

MathML 2.0

<!DOCTYPE math PUBLIC "-//W3C//DTD MathML 2.0//EN" "http://www.w3.org/TR/MathML2/dtd/mathml2.dtd">

MathML 1.01

<!DOCTYPE math SYSTEM "http://www.w3.org/Math/DTD/mathml1/mathml.dtd">

HTML 4.01

HTML 4.01 came in the same three versions XHTML 1.0 did a few years later.

Strict

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">

Transitional

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

Frameset

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Frameset//EN" "http://www.w3.org/TR/html4/frameset.dtd">

HTML 3.2

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">

HTML 2.0

<!DOCTYPE html PUBLIC "-//IETF//DTD HTML 2.0//EN">
X

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