How to use the recommonmark.transform.AutoStructify.suffix_set function in recommonmark

# title = ref.children[0].astext()
        uri = ref['refuri']
        if uri.find('://') != -1:
            return (title, uri, None)
        anchor = None
        arr = uri.split('#')
        if len(arr) == 2:
            anchor = arr[1]
        if len(arr) > 2 or len(arr[0]) == 0:
            return (title, uri, None)
        uri = arr[0]

        abspath = os.path.abspath(os.path.join(self.file_dir, uri))
        relpath = os.path.relpath(abspath, self.root_dir)
        suffix = abspath.rsplit('.', 1)
        if len(suffix) == 2 and suffix[1] in AutoStructify.suffix_set and (
                os.path.exists(abspath) and abspath.startswith(self.root_dir)):
            # replace the path separator if running on non-UNIX environment
            if os.path.sep != '/':
                relpath = relpath.replace(os.path.sep, '/')
            docpath = '/' + relpath.rsplit('.', 1)[0]
            # rewrite suffix to html, this is suboptimal
            uri = docpath + '.html'
            if anchor is None:
                return (title, uri, docpath)
            else:
                return (title, uri + '#' + anchor, None)
        else:
            # use url resolver
            if self.url_resolver:
                uri = self.url_resolver(relpath)
            if anchor: