You can find the W3C XHTML 1.0 Specification at http://www.w3.org/TR/xhtml1/
World Wide Web Consortium web site : http://www.w3.org
The document located at http://www.metis-light.com/ was checked and found to be valid XHTML 1.0 Strict.
This means that the resource in question identified itself as "XHTML 1.0 Strict" and that we successfully performed a formal validation using an SGML or XML Parser (depending on the markup language used).
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You can find the W3C XHTML 1.0 Specification at http://www.w3.org/TR/xhtml1/