Trovato!

Va modificata la riga DOCTYPE da

codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1 Strict//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
a
codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN " 
   "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd ">