is_referencing_order
Use it like this:
- [ #is/_referencing_order :: Order] or
- [ is_referencing_order :: Order]
The Order(s) related to this Invoice. One or more Orders may be combined into a single Invoice.
Relation describes that: [ #has_/domain :: Invoice] ( #has_/name :: is_referencing_order) ( #has_/range :: Order)