def parse_set_header(value, on_update=None):
    if not value:
        return HeaderSet(None, on_update)
    return HeaderSet(parse_list_header(value), on_update)
Parse a set-like header and return a :class:`HeaderSet` object:
dataset/ETHPy150Open IanLewis/kay/kay/lib/werkzeug/http.py/parse_set_header