Standards or Quirks?

Composing a correct DOCTYPE declaration could be a daunting process (see DOCTYPE Switch Browser Comparison). Miss a fully-qualified URI and your browser starts doing something you didn't expect.

Can you tell by looking at a DOCTYPE declaration if you're triggering the Standards mode? Or is it still in Quirks? You can look up DOCTYPEs W3C or elsewhere, but a slight omission in the declaration leaves you to the mercy of the browser because it has it own logic of deciding what mode to switch to.

For example, Eric Meyer provided some in his article Picking a Rendering Mode. See how tricky it gets? Also, check out Mozilla's DOCTYPE sniffing. Now that's a can of worms, if you ask me.

A found a handy little script at Mozilla to help troubleshoot rendering modes. The same article, Mozilla's DOCTYPE sniffing, points to a page that utilizes the script.

<div>
The DOM says we are in
<script type="text/javascript">
    var mode = document.compatMode;
    var output= "<span>" + mode + "</span>";
    document.write(output);
</script>
mode.
</div>

Or you could shorten it for better readability:

<div>
The DOM says we are in
<script type="text/javascript">
    document.write (document.compatMode);
</script>
mode.
</div>

The output is pretty much the same across all modern browsers. In Standards mode IE6/Win, Netscape 6+/Mozilla and Opera return "CSS1Compat". In Quirks mode IE6/Win and Mozilla report "BackCompat", while Opera says "QuirksMode".