old_contents: """Pytac: Python Toolkit for Accelerator Controls."""
  
  # PV types
  SP = 'setpoint'
  RB = 'readback'
  # Unit systems
  ENG = 'engineering'
  PHYS = 'physics'
  # Model types.
  SIM = 'simulation'
  LIVE = 'live'
  
new_contents: """Pytac: Python Toolkit for Accelerator Controls."""
  
  # PV types
  SP = 'setpoint'
  RB = 'readback'
  # Unit systems
  ENG = 'engineering'
  PHYS = 'physics'
  # Model types.
  SIM = 'simulation'
  LIVE = 'live'
  
  from . import device, element, lattice, load_csv, lattice, utils
  
subject: Add modules to pytac namespace.