Hello M.,
It is not yet possible; You are right...
It is not yet implemented...
1/ But for example cardinality and qualified associations inherited of arrow style... as:
@startuml
<style>
arrow {
FontColor Blue
FontSize 14
FontStyle bold
BackgroundColor pink
}
</style>
interface Map<K,V>
class HashMap<Long,Customer>
Map <|.. HashMap
Shop [customerId: long] ---> "customer\n1" Customer
HashMap [id: Long] -r-> "value" Customer
@enduml
2/ But that can be a good wanted feature...
If that can help,
Regards,
Th.