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Explanation

The purge command can be used to delete many messages at once. 
/purge <amount>

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Flags

Our purge command currently has two flags:
  • --before=<message_id>: This flag will delete all messages before the message with the given ID.
  • --after=<message_id>: This flag will delete all messages after the message with the given ID.
So for example, you can do: 
/purge <amount> --flag=<message_id>