if (mark <= gapStart) return mark; else return mark - (gapEnd - gapStart);
int res = mark; if (mark > gapStart) res -= (gapEnd - gapStart); return res; }
    public int getOffset()    {      // Check precondition.      assert mark <= gapStart || mark >= gapEnd : "mark: " + mark                                               + ", gapStart: " + gapStart                                               + ", gapEnd: " + gapEnd;      if (mark <= gapStart)        return mark;      else        return mark - (gapEnd - gapStart);    }