If you use deprecated attributes or tags <center>, <font color="red">, or <td valign="top"> etc. in XHTML 1.0 Strict (no depr. attributes), modern browsers (I will use Chrome as an example) still take notice of and use them.
If you use HTML5 <video> on an XHTML 1.0 Strict DOCTYPE Chrome will still recognize it - it's not as if they'd program it to not. I tested the worst deprecated, capitalized, and unquoted attribute code I could write, along with HTML5 audio, with the XHTML 1.0 Strict DOCTYPE in Chrome and it rendered flawlessly.
Here's the code I tested, working flawlessly in Chrome (red bg, centered table, audio playing):
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>Do browsers care about the DOCTYPE?</title>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" >
</head>
<body bgcolor=#ff0000>
<CENTER>
<table cellpadding="0" cellspacing=0>
<tr><td valign=top>test</td></tr>
</table>
</CENTER>
and some HTML5 audio..
<audio autoplay>
<source src="http://www.duncannz.com/resources/sound/alarm.mp3" type="audio/mp3">fallback text</audio>
</body>
</html>
So my question: Do modern browsers (translation: browsers other than IE) pay any attention at all, or do anything differently, because of the DOCTYPE? Do they even bother to read and interpret it?
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