-A hash reference of additional string substitutions
-
-=item sub_param
-
-A hash reference, keys are the names of existing substitutions,
-values are an addition parameter object to pass to the subroutine
-for that substitution, e.g.
-
- 'sub_param' => {
- 'payment_history' => {
- 'start_date' => 1434764295,
- },
- },