You can organize sequence diagrams to better represent a system.
You can reorder messages, delay asynchronous messages, as well as manage combined
fragments and lifelines.
Reordering lifelines and messages in sequence diagrams
In sequence diagrams, you can reorder lifelines or move
a message across other messages and interaction fragments on the same
lifeline or on another lifeline to reorder the sequence in which the
messages occur. After you reorder a message, the message number automatically
indicates the updated position on the lifeline.