13 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:dc="http://purl.org/dc/elements/1.1/"
    xmlns:dct="http://purl.org/dc/terms/"
    xmlns:bibo="http://purl.org/ontology/bibo/"
    xmlns:daia="http://purl.org/ontology/daia/"
    xmlns:frbr="http://purl.org/vocab/frbr/core#"
    xmlns:isbd="http://iflastandards.info/ns/isbd/elements/"
    xmlns:gn="http://www.geonames.org/ontology#"
    xmlns:lv="http://purl.org/lobid/lv#"
    xmlns:marcrel="http://id.loc.gov/vocabulary/relators/"
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:owl="http://www.w3.org/2002/07/owl#"
    xmlns:geo="http://www.opengis.net/ont/geosparql#"
    xmlns:foaf="http://xmlns.com/foaf/0.1/">
  <head>
    <title>Hello World!</title>
  </head>
  <body>
    <h1>Hello World!</h1>
  </body>
</html>