gapEnd += nitems;
  public UndoableEdit remove(int where, int nitems) throws BadLocationException    {    // check arguments    int length = length();    if (where >= length)      throw new BadLocationException("the where argument cannot be greater"                                     + " than the content length", where);    if ((where + nitems) > length)      throw new BadLocationException("where + nitems cannot be greater"          + " than the content length", where + nitems);    // check if we are at the gap boundary    if (where != gapStart)      shiftGap(where);    // now we simply have to enlarge the gap    gapEnd += nitems;	return null;    }