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Asked: 2026-05-30T02:06:20+00:00

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

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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?

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1 Answer

  1. Editorial Team

    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.

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