Updated tutorial: Serving XHTML 1.0
This tutorial was updated to reflect the fact that IE7 no longer flips into quirks mode when an XML declaration is used. For a detailed list of changes read the full post.
The following paragraphs were changed as shown by the ins and del markup.
<p>In browsers such as <ins>Internet Explorer 7, Firefox,</ins><del>Mozilla</del>, Netscape, Opera, and others, with or without the XML declaration, a page served with a DOCTYPE declaration will be rendered in standards mode.</p>
<p> With Internet Explorer<ins> 6</ins>, however, if anything appears before the DOCTYPE declaration the page is rendered in quirks mode. </p>
<p>Because Internet Explorer <ins> 6</ins> users <ins>still</ins> count for a very large proportion of browser users, this is a significant issue. If you want to ensure that your pages are rendered in the same way on all standards-compliant browsers, you need to think carefully about how you deal with this.</p>
<p>The presence of an XML declaration in an XHTML 1.0 file served as HTML will cause your file to be rendered in quirks mode on Internet Explorer <ins> 6</ins> (and therefore for a potentially large proportion of your audience).</p>