def p_schema(p):
    """schema : schema schema_base_elems
              | schema_base_elems
    """
    if len(p) == 2:
        p[0] = p[1]
    elif isinstance(p[1], list):
        p[0] = p[1] + [p[2]]
    else:
        p[0] = [p[1], p[2]]
