default namespace = "http://www.w3.org/1999/xhtml"
   namespace epub = "http://www.idpf.org/2007/ops"
      
   include "epub-xhtml-30.rnc" {   
        html5.nav.content = html5.headings.class?, html5.ol     
        html5.oli.content = html5.a.phrasing | ((html5.a.phrasing | html5.span), html5.ol)
   }