Hello C., and all,
Here are some examples:
Code | Output |
skinparam stereotypePosition top
participant A<<st>>
participant B<<st2>>
A --> B : test stereo |  |
skinparam stereotypePosition bottom
participant A<<st>>
participant B<<st2>>
A --> B : test stereo
|  |
But FYI that concerns only sequence diagram...
If that can help;
Regards,
Th.