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.