Method Calendar.Event.Day_Event()->scan_jd()
- Method scan_jd
 intscan_jd(Calendar.Calendarrealm,intjd,int(-1..-1)|int(1..1)direction)- Description
 This method has to be defined, and is what really does some work.
- Parameter 
direction 1Forward (next),
-1Backward (previous).
- Returns
 It should return the next or previous julian day (>jd) when the event occurs, or the constant NODAY if it doesn't.