@pimms.param<EOL><INDENT>def registration(r):<DEDENT>
if r is None: return '<STR_LIT>'<EOL>if not pimms.is_str(r):<EOL><INDENT>raise ValueError('<STR_LIT>')<EOL><DEDENT>return r<EOL>
proj.registration is either None or the name of a registration that should be used as the
base sphere for the given map projection; note that None and 'native' are equivalent.