A selection of ongoing transactions.

Input Format:

A set of one or more of the following:

• source - A telescope positioning command.
• mark - A mark command. A mark command is assumed to be completed when its effects have been recorded in at least one frame.
• flux - A request_flux operation.
• focus
  Context:
  The acquired command returns an indication of the status of one or more ongoing transactions. The user tells it which transactions to report on via an AcquireTargets argument.