code: public List<CmsJspNavElement> getNavigationForFolder(String folder, int level) {
  
          folder = CmsResource.getFolderPath(folder);
          // If level is one just use root folder
          if (level == 0) {
              return getNavigationForFolder("/");
          }
          String navfolder = CmsResource.getPathPart(folder, level);
          // If navigation folder found use it to build navigation
          if (navfolder != null) {
              return getNavigationForFolder(navfolder);
          }
          // Nothing found, return empty list
          return Collections.<CmsJspNavElement> emptyList();
      }
docs: Build a navigation for the folder that is either minus levels up
  from the given folder, or that is plus levels down from the
  root folder towards the given folder.<p>
  
  If level is set to zero the root folder is used by convention.<p>
  
  @param folder the selected folder
  @param level if negative, walk this many levels up, if positive, walk this many
  levels down from root folder
  
  @return a sorted (ascending to navigation position) list of navigation elements