code: public static boolean registerURLRewriter( ServletRequest request, URLRewriter rewriter )
      {
          ArrayList/*< URLRewriter >*/ rewriters = getRewriters( request );
  
          if ( rewriters == null )
          {
              rewriters = new ArrayList/*< URLRewriter >*/();
              rewriters.add( rewriter );
              request.setAttribute( URL_REWRITERS_KEY, rewriters );
          }
          else
          {
              return addRewriter( rewriters, rewriter, rewriters.size() );
          }
  
          return true;
      }
docs: Register a URLRewriter (add to a list) in the request.  It will be added to the end
  of a list of URLRewriter objects and will be used if {@link #rewriteURL} is called.
  
  @param request  the current ServletRequest.
  @param rewriter the URLRewriter to register.
  @return <code>false</code> if a URLRewriter has been registered
  that does not allow other rewriters. Otherwise, <code>true</code>
  if the URLRewriter was added to the chain or already exists in
  the chain.