code: def add_format(mimetype, format, requires_context=False):
  	
  	global formats
  	global ctxless_mimetypes
  	global all_mimetypes
  	formats[mimetype] = format
  	if not requires_context:
  		ctxless_mimetypes.append(mimetype)
  	all_mimetypes.append(mimetype)
docs: Registers a new format to be used in a graph's serialize call
  	    If you've installed an rdflib serializer plugin, use this
  	    to add it to the content negotiation system
  	    Set requires_context=True if this format requires a context-aware graph