You're seeing just the callback configure, go back to Broadway.Acknowledger module for more information.
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configure(ack_ref, ack_data, options)

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configure(ack_ref :: term(), ack_data :: term(), options :: keyword()) ::
  {:ok, new_ack_data :: term()}

Configures the acknowledger with new options.

Every acknowledger can decide how to incorporate the given options into its ack_data. The ack_data is the current acknowledger's data. The return value of this function is {:ok, new_ack_data} where new_ack_data is the updated data for the acknowledger.

Note that options are different for every acknowledger, as the acknowledger is what specifies what are the supported options. Check the documentation for the acknowledger you're using to see the supported options.