Done, slightly simpler but same idea. Thanks!

It is possible to have a number of date parts other than 3. For 
example, when initialising a form ($this):

     $this->addVariable(_("Start Date"), 'start', 'monthDayYear', true);
     $this->addVariable(_("Start Time"), 'start', 'hourMinuteSecond', true);

Which works as expected, but breaks the validation function, which 
should probably read:

     function emptyDateArray($date)
     {
         if (!is_array($date)) {
             return empty($date);
         }

         $empty = 0;
         $parts = 0;
         /* Check each date array component. */
         foreach ($date as $key => $val) {
             $parts++;
             if (empty($val)) {
                 $empty++;
             }
         }
         /* Check state of empty. */
         if ($empty == 0) {
             /* If no empty parts return 0. */
             return 0;
         } elseif ($empty == $parts) {
             /* If all empty parts return 1. */
             return 1;
         } else {
             /* If some empty parts return -1. */
             return -1;
         }
     }