new_contents: """Engine related decorators."""
  from . import get_engine_manager
  
  
  def register(cls):
      """Register an engine extension metadata.
  
      Parameters
      ----------
      cls: ABCEngineExtension
        a subclass of base extension metadata type
      """
      # Register the given class on the current engine manager.
      get_engine_manager().register(cls)
      return cls
  
subject: Add missing files.