code: def _get_default_projection(cls):
  		
  		
  		projected = []  # The fields explicitly requested for inclusion.
  		neutral = []  # Fields returning neutral (None) status.
  		omitted = False  # Have any fields been explicitly omitted?
  		
  		for name, field in cls.__fields__.items():
  			if field.project is None:
  				neutral.append(name)
  			elif field.project:
  				projected.append(name)
  			else:
  				omitted = True
  		
  		if not projected and not omitted:
  			# No preferences specified.
  			return None
  			
  		elif not projected and omitted:
  			# No positive inclusions given, but negative ones were.
  			projected = neutral
  		
  		return {field: True for field in projected}
docs: Construct the default projection document.