/** Adds an editor to the current collection of active editors, and makes it a tab pane. */
 void addEditor(PluggableEditor ed) {
   if (activeEditors.contains(ed) == false) // don't add editors twice!
   {
     add(ed);
     ed.registerComponents(
         registerMenu, registerButtons, registerTree, registerTreeMenu, registerJX);
   }
 }