Sequence: Create/Destroy Participants
Mermaid's own create/destroy example: Carl and Donald appear at the message that creates them, and Carl and Bob's lifelines end with a cross at the message that destroys them — useful for showing a participant's actual lifetime instead of assuming every actor exists for the whole diagram.
sequence-create-destroy-participants.mmd
sequenceDiagram
Alice->>Bob: Hello Bob, how are you ?
Bob->>Alice: Fine, thank you. And you?
create participant Carl
Alice->>Carl: Hi Carl!
create actor D as Donald
Carl->>D: Hi!
destroy Carl
Alice-xCarl: We are too many
destroy Bob
Bob->>Alice: I agree