hi,I saw nothing about different content types in the XHTML section.(In fact, w3schools.org pages are served as text/html, not as xml.)I recommand those readings about the importance of content-types in XHTML :* http://www.webdevout.net/articles/beware_of_xhtml.php* http://hixie.ch/advocacy/xhtmlIn short, when you send XHTML as text/html (and IE shows a download prompt if you send the correct content-type), the browser parses it as an HTML document, and it understands new things like the self-closing tags as old HTML errors. So it's even harder to parse than an old well-formed HTML document.Served as text/html, XHTML is as useful as HTML4.01 strict, maybe a little more strict, even if you can write strict HTML4.01 documents too.XHTML is really needed when you need to mix multiple XML documents, as XHTML+MathML+SVG (see http://www.w3.org/TR/XHTMLplusMathMLplusSVG/ ).I hope it'll help tou to correct your XHTML lessons.Good luck.