tutorial/tutorial3.xxe_gui:

  <tool name="countWordsTool">
    <class>CountWordsTool</class>
  </tool>

  <statusBar name="statusBar">
    <tool name="countWordsTool" />
    <insert />
  </statusBar>

The custom tool implemented by Java™ class CountWordsTool (code contained in XXE_install_dir/doc/gui/tutorial/custom_parts.jar) is declared using a tool element.

Then this tool is inserted in the standard status bar (statusBar element called "statusBar" found in DesktopApp.xxe_gui), before all the other components of this status bar, by the means of the <insert/> facility.