Hello B.,
A possible workaround is to use sub-diagram and label, as:
@startuml
frame "state_machine" {
label l [
{{
state foo
state bar
[*] -> foo
foo -> bar
}}
]
}
@enduml
Or simply `mainframe`, as:
@startuml
mainframe "state_machine"
state foo
state bar
[*] -> foo
foo -> bar
@enduml
If that can help,
Regards,
Th.