Hello O.,
You can currently use sub-diagram, `{{` and `}}`, as:
@startuml
start
:Choose Menu;
repeat
:Choose menu item;
repeatwhile
:Confirm Order;
note right
{{
start
:Provide payment
details;
:Provide shipment
details;
stop
}}
end note
stop
@enduml
If that can help,
Regards,
Th.