When trying to set the position of the constraint on a datebox with 'after_start', 'after_end', 'before_start' or 'before_end'
it throws an Exception
Whereas the positions 'start_after', 'start_before', 'end_after' or 'end_before' works.
The problem is in the parseConstraint method of org.zkoss.zul.SimpleDateConstraint, where its checks if the constraint start with 'before'/'after', then tries to parseDate the end of the constraint.
A solution would be to check if the constraint is a position 'before_', 'after_', ... or to check if the end of the constraint starts with ''.