Mermaid Sequence Diagram with MAIDR

Left and right walk the messages in time; down moves onto each participant's lifeline, keeping the moment. The rotor's Fragments unit jumps between loops and alternatives.

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sequenceDiagram
  autonumber
  actor U as User
  participant W as Web app
  participant D as Database
  U->>W: Log in
  loop Until the password matches
    W->>D: Find user
    D-->>W: User row
  end
  alt Two-factor enabled
    W-->>U: Ask for a code
  else
    W-->>U: Welcome
  end
  Note over W: Session stored