protected IndexedRegion getCorrespondingNode(IStructuredDocumentRegion sdRegion) {
   IStructuredModel sModel =
       StructuredModelManager.getModelManager().getExistingModelForRead(fDocument);
   IndexedRegion indexedRegion = null;
   try {
     if (sModel != null) indexedRegion = sModel.getIndexedRegion(sdRegion.getStart());
   } finally {
     if (sModel != null) sModel.releaseFromRead();
   }
   return indexedRegion;
 }