def id_prefix(tag_name):
    """return the id attribute prefix for the tag name"""
    id_prefix_map = {
        "mml:math": "m",
        "disp-formula": "equ",
        "fig": "fig",
        "table-wrap": "table",
        "media": "video",
    }
    return str(id_prefix_map.get(tag_name))