code: public ElementBase register(String path, String url) throws Exception {
          return register(path, url, null);
      }
docs: Register a plugin by specifying a path and a url.
  
  @param path Format is &lt;tab name&gt;\&lt;tree node path&gt;
  @param url Main url of plugin.
  @return Container created for the plugin.
  @throws Exception Unspecified exception.