/*
  * (non-Javadoc)
  *
  * @see org.eclipse.wst.sse.ui.views.contentoutline.ContentOutlineConfiguration#getMenuListener(org.eclipse.jface.viewers.TreeViewer)
  */
 public IMenuListener getMenuListener(TreeViewer viewer) {
   IMenuListener listener = null;
   if (fMenuHelper == null && viewer.getInput() instanceof DTDModelImpl) {
     fMenuHelper = new DTDContextMenuHelper((DTDModelImpl) viewer.getInput());
     fMenuHelper.createMenuListenersFor(viewer);
   }
   if (fMenuHelper != null) {
     listener = fMenuHelper.getMenuListener();
   }
   return listener;
 }
 /*
  * (non-Javadoc)
  *
  * @see org.eclipse.wst.sse.ui.views.contentoutline.ContentOutlineConfiguration#unconfigure(org.eclipse.jface.viewers.TreeViewer)
  */
 public void unconfigure(TreeViewer viewer) {
   super.unconfigure(viewer);
   fViewerContributions.remove(viewer);
   if (fMenuHelper != null) {
     fMenuHelper.removeMenuListenersFor(viewer);
     fMenuHelper = null;
   }
 }