Introduction

Doctypes - short for ‘document type’ - help browsers to understand the version of HTML the document is written in for better interpretability. Doctype declarations are not HTML tags and belong at the very top of a document. This topic explains the structure and declaration of various doctypes in HTML.

Syntax

• <!DOCTYPE [version-specific string]>

Remarks

The <!DOCTYPE> declaration is not an HTML tag. It is used for specifying which version of HTML the document is using. This is referred to as the document type declaration (DTD).

The <!DOCTYPE> declaration is NOT case sensitive. To check if the HTML of your Web pages is valid, go to W3C’s validation service.

• Some old versions of IE don’t support some HTML tags unless a proper doctype is available.
• It’s vital that a doctype is declared as to make sure the browser doesn’t use quirks mode. More info on MDN.

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