def renderable(tiddler, environ=None):
    """
    Return true if the provided tiddler's type is one
    that can be rendered by the wikitext render subsystem.
    """
    if not environ:
        environ = {}
    return (not tiddler.type
            or tiddler.type == 'None'
            or tiddler.type
                in environ.get('tiddlyweb.config', {}).get(
                    'wikitext.type_render_map', []))