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Hello O.,
1/ Firstly no, only:
See:
2/ Secondly yes, with adding sub-diagram as:
participant "{{\n[component A]\n}}" as A
If that can help,Regards,Th.
Just to point out that the outer boxes in Th's example can be styled out, at the cost of a small gap between the component and the lifeline.
Maybe you want to use it in C4-Stdlib context, the new released C4-StdLib v 2.7.0 supports sequence diagrams too (incl. themes)
It is also merged into plantuml-stdlib that `!include <C4/C4_Sequence>` can be used in the next version PlantUML v1.2023.11 too.
BR Helmut