Without INTERVAL=WORKDAY, the 5-day Christmas break would be scheduled through the weekend. 

                                                     Calendar of Holidays Only                                                     1

  -------------------------------------------------------------------------------------------------------------------------------
  |                                                                                                                             |
  |                                                        January  1997                                                        |
  |                                                                                                                             |
  |-----------------------------------------------------------------------------------------------------------------------------|
  |     Sunday      |     Monday      |     Tuesday     |    Wednesday    |    Thursday     |     Friday      |    Saturday     |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |                 |                 |                 |        1        |        2        |        3        |        4        |
  |                 |                 |                 |***New Year's****|                 |                 |                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |        5        |        6        |        7        |        8        |        9        |       10        |       11        |
  |                 |                 |                 |                 |                 |                 |                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |       12        |       13        |       14        |       15        |       16        |       17        |       18        |
  |                 |                 |                 |                 |                 |                 |                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |       19        |       20        |       21        |       22        |       23        |       24        |       25        |
  |                 |                 |                 |                 |                 |                 |                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |       26        |       27        |       28        |       29        |       30        |       31        |                 |
  |                 |                 |                 |                 |                 |                 |                 |
  -------------------------------------------------------------------------------------------------------------------------------
                                                     Calendar of Holidays Only                                                     2

  -------------------------------------------------------------------------------------------------------------------------------
  |                                                                                                                             |
  |                                                       February  1997                                                        |
  |                                                                                                                             |
  |-----------------------------------------------------------------------------------------------------------------------------|
  |     Sunday      |     Monday      |     Tuesday     |    Wednesday    |    Thursday     |     Friday      |    Saturday     |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |                 |                 |                 |                 |                 |                 |        1        |
  |                 |                 |                 |                 |                 |                 |                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |        2        |        3        |        4        |        5        |        6        |        7        |        8        |
  |                 |                 |                 |                 |                 |                 |                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |        9        |       10        |       11        |       12        |       13        |       14        |       15        |
  |                 |                 |                 |                 |                 |                 |                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |       16        |       17        |       18        |       19        |       20        |       21        |       22        |
  |                 |                 |                 |                 |                 |                 |                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |       23        |       24        |       25        |       26        |       27        |       28        |                 |
  |                 |                 |                 |                 |                 |                 |                 |
  -------------------------------------------------------------------------------------------------------------------------------
                                                     Calendar of Holidays Only                                                    12

  -------------------------------------------------------------------------------------------------------------------------------
  |                                                                                                                             |
  |                                                       December  1997                                                        |
  |                                                                                                                             |
  |-----------------------------------------------------------------------------------------------------------------------------|
  |     Sunday      |     Monday      |     Tuesday     |    Wednesday    |    Thursday     |     Friday      |    Saturday     |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |                 |        1        |        2        |        3        |        4        |        5        |        6        |
  |                 |                 |                 |                 |                 |                 |                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |        7        |        8        |        9        |       10        |       11        |       12        |       13        |
  |                 |                 |                 |                 |                 |                 |                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |       14        |       15        |       16        |       17        |       18        |       19        |       20        |
  |                 |                 |                 |                 |                 |                 |                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |       21        |       22        |       23        |       24        |       25        |       26        |       27        |
  |                 |                 |                 |                 |*Christmas Break*|*Christmas Break*|                 |
  |-----------------+-----------------+-----------------+-----------------+-----------------+-----------------+-----------------|
  |       28        |       29        |       30        |       31        |                 |                 |                 |
  |                 |*Christmas Break*|*Christmas Break*|*Christmas Break*|                 |                 |                 |
  -------------------------------------------------------------------------------------------------------------------------------