def add_format(self, mimetype, format, requires_context=False):
self.formats[mimetype] = format<EOL>if not requires_context:<EOL><INDENT>self.ctxless_mimetypes.append(mimetype)<EOL><DEDENT>self.all_mimetypes.append(mimetype)<EOL>
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