code: public void setDayExcluded (final Calendar day, final boolean exclude)
    {
      if (exclude)
      {
        if (isDayExcluded (day))
        {
          return;
        }
  
        m_aExcludeDays.add (day);
        m_bDataSorted = false;
      }
      else
      {
        if (!isDayExcluded (day))
        {
          return;
        }
  
        removeExcludedDay (day, true);
      }
    }
docs: <p>
  Redefine a certain day to be excluded (true) or included (false).
  </p>