@Override
  public String toString() {
    return "HighlightingSessionImpl: " +
           "myVisibleRange:"+myVisibleRange+
           "; myPsiFile: "+myPsiFile+ " (" + myPsiFile.getClass() + ")"+
           (myIsEssentialHighlightingOnly ? "; essentialHighlightingOnly":"");
  }
@Override
  public String toString()