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