10 prefixes (rdfa)

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN" "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd">
<html xml:lang="en"
    xmlns="http://www.w3.org/1999/xhtml"
    xmlns:owl="http://www.w3.org/2002/07/owl#"
    xmlns:foaf="http://xmlns.com/foaf/0.1/"
    xmlns:oo="http://purl.org/openorg/"
    xmlns:dcterms="http://purl.org/dc/terms/"
    xmlns:geo="http://www.opengis.net/ont/geosparql#"
    xmlns:skos="http://www.w3.org/2004/02/skos/core#"
    xmlns:org="http://www.w3.org/ns/org#"
    xmlns:xtypes="http://purl.org/xtypes/"
    xmlns:lyou="http://purl.org/linkingyou/"
    xmlns:vcard="http://www.w3.org/2006/vcard/ns#">
  <head>
    <title>Hello World!</title>
  </head>
  <body>
    <h1>Hello World!</h1>
  </body>
</html>