code: public void initializeRelativePath(ServletRequest request, String relativeTo) 
      {
          if ( relativeTo == null )
          {
              relativeTo = _relativeTo;
          }
  
          if ( relativeTo == null ) return;
  
          assert ! relativeTo.endsWith("/") : relativeTo;
          String path = getPath();
           
          // If this is a local (relative) path, prefix it with the given 'relativeTo' path, and save a flag.
          // We save this flag in a local variable because the Forward object may be saved/restored for use again.
          if (! getContextRelative() && ! FileUtils.isAbsoluteURI(path)) {
              assert path.startsWith("/") : path;
              setPath(relativeTo + path);
              setContextRelative(true);
              _outsidePageFlowDirectory = true;
          }
          
          // Store a flag in the request that will prevent another page flow from being initialized implicitly because
          // we're hitting a path within it.  We want to stay in the context of the current page flow.
          if (_outsidePageFlowDirectory) {
              PageFlowRequestWrapper.get(request).setStayInCurrentModule(true);
          }
      }
docs: If this is a local path, change it so it's relative to the given path prefix, and remember that we did it in
  a flag (_outsidePageFlowDirectory).  This is a framework-invoked method that should not normally be called
  directly.