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Possible Duplicate:
What's up, Doctype?
HTML: What is the functionality of !DOCTYPE

Okay, when I first learn HTML, I basically learn from trial and error as I went along, and didn't really sit down to properly learn it as far as I can remember. As a result of this, I've missed out a lot, and therefore, I've decided to start from the basics for my own benefit. :) So here I am, (re-)learning HTML.

Now, my question - the <!DOCTYPE> tag confuses me more than any other HTML tag I've ever come across, so I've come here to clear up any questions I have regarding it so I can use it confidently. :)

Firstly, can someone explain to me why it's necessary to use a <!DOCTYPE> tag in your webpages? They work fine without them, don't they? I've read that it is so it can be validated against the standards of the W3C, but that's all I know. A little more detail would be appreciated. :)

Secondly, after reading up on it, I'm still confused as to what exactly goes in my <!DOCTYPE> and how to type it out. For example, this is one kind of DOCTYPE I've seen used:

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

Yet I've also seen other variations, and from what I've read, there are different DOCTYPES to validate against - it's all so very confusing, which should I use in my webpages if I was going to use one?

Community
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Hashim Aziz
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4 Answers4

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W3C has a pretty good answer to this at http://www.w3.org/QA/Tips/Doctype

Why?

Why specify a doctype? Because it defines which version of (X)HTML your document is actually using, and this is a critical piece of information needed by some tools processing the document.

For example, specifying the doctype of your document allows you to use tools such as the Markup Validator to check the syntax of your (X)HTML. Such tools won't be able to work if they do not know what kind of document you are using.

But the most important thing is that with most families of browsers, a doctype declaration will make a lot of guessing unnecessary, and will thus trigger a "standard" rendering mode.

Basically if you leave it out, the browser will try and guess what rendering mode to use, and it might cause some unexpected results.

JYelton
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it basically tells the browser how to interpret the page you're sending it. If you don't send anything, it has to make guesses. Some constructs are valid in a format while invalid in others, etc. Some browsers may display your page correctly while others don't. So yes, do choose and send a DOCTYPE.

There are several doctypes you can use, xhtml, html strict, html transitional, 4.01, etc. You can see a list of valid types here ... http://www.w3.org/QA/2002/04/valid-dtd-list.html

Rodolfo
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The declaration refers to a Document Type Definition (DTD). A DTD specifies the rules for the markup language, so that the browsers render the content correctly.

Going forward, for html5 compliance, the correct tag is simply:

<!DOCTYPE html>
OnResolve
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You set a doctype to say to your browser or somthing else what you going tho do. Its look like what you do whit a business card

There are several doctype's. The most yoused doctype's are transitional: 

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

The some stricter doctype is: (see "strict") 

  <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

Also you can youse a speciffie doctype declaraition for youse a frameset. But this is outdated, frameset is a unnecessary for my but i will show you the doctype for this. But forgot the framesets this is an not useful html element whit html5. Here see you the follow frameset doctype: 

   <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"

"http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">

And at last. You can youse a language attribuut for your the doctypes. This can youse by html and xhtml. 

  <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
Raymond van Os
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