code: def add_format(self, mimetype, format, requires_context=False):
  		
  		self.formats[mimetype] = format
  		if not requires_context:
  			self.ctxless_mimetypes.append(mimetype)
  		self.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