code: public ElementBase register(String path, PluginDefinition def) throws Exception {
          return register(path, def, null);
      }
docs: Registers the plugin with the specified definition with the specified path. If a tree path is
  absent, the plugin is associated with the tab itself.
  
  @param path Format is &lt;tab name&gt;\&lt;tree node path&gt;
  @param def Plugin definition
  @return The newly created plugin.
  @throws Exception Unspecified exception.