@Override
 public boolean append(RuleFragment frag) {
   if (frag instanceof NamedFragment) {
     NamedFragment nf = (NamedFragment) frag;
     if (nf.getName().equals(this.getName())) {
       this.setOccurences(this.getOccurences().add(nf.getOccurences()));
       return true;
     }
   }
   return false;
 }