old_contents: class ArgumentValidationError(Exception):
      pass
  
  
  class ArgumentTypeValidationError(Exception):
      pass
  
new_contents: """phial's custom errors."""
  
  
  class ArgumentValidationError(Exception):
      """Exception indicating argument validation has failed."""
  
      pass
  
  
  class ArgumentTypeValidationError(Exception):
      """Exception indicating argument type validation has failed."""
  
      pass
  
subject: Add docstrings