




Default value: 
(when (> *delivery-level* 0) :delete)
Do not delete any condition class. This is the default at severity = 0.
Delete unwanted conditions. If an error for a deleted condition is signaled, it is signalled as a simple error condition, with the arguments in the 
format-arguments
 slot. This is the default at severity > 0. 
Redirect unwanted conditions to the first parent in their hierachy which is not deleted.