Web Application Doctype

[Dysan]

What DOCTYPE should be used, for a web application?
What are the different DOCTYPES available, and what are they for?

[bradgrafelman]

See this W3C page: Recommended list of DTDs (http://www.w3.org/QA/2002/04/valid-dtd-list.html)

EDIT: As well as this W3C page: Tips for Webmasters :: Doctypes (http://www.w3.org/QA/Tips/Doctype)

[NogDog]

Also see Section 7.1 and 7.2 (http://www.w3.org/TR/html4/struct/global.html#h-7.1) of the HTML Spec. as to why. Another very important reason is that using a fully qualified document type declaration (if it is the very first line of the document) gets IE out of "quirks mode" and into a fairly standards-compliant mode with regard to the rendering of block type elements, making it much easier to get your pages to render the same in IE and other browsers.