setPositionsInRange(newGapStart, gapStart - newGapStart, gapStart);
setPositionsInRange(newGapStart, gapStart, false);
  protected void shiftGapStartDown(int newGapStart)  {    if (newGapStart == gapStart)      return;    assert newGapStart < gapStart : "The new gap start must be less than the "                                    + "old gap start.";    setPositionsInRange(newGapStart, gapStart - newGapStart, gapStart);    gapStart = newGapStart;  }