old_contents: pipeline_functions = {}
  
  
  def register_pipeline(function):
      if function.__name__ in pipeline_functions:
          raise ExistingFunctionError(
              '%s is already registered with %s.%s' % (
                  function.__name__, function.__module__, function.__name__))
      pipeline_functions[function.__name__] = function
      return function
  
  
  class ExistingFunctionError(Exception):
      pass
  
new_contents: pipeline_functions = {}
  
  
  def register_pipeline(function):
      """Decorator to register a function for the assembly pipeline."""
      if function.__name__ in pipeline_functions:
          raise ExistingFunctionError(
              '%s is already registered with %s.%s' % (
                  function.__name__, function.__module__, function.__name__))
      pipeline_functions[function.__name__] = function
      return function
  
  
  class ExistingFunctionError(Exception):
      pass
  
subject: Add minimal docstring for decorator