Help me add documentation to this bigquery user defined function (UDF)

CREATE FUNCTION core.fn_fun001_card_format(f1 STRING, f2 STRING, f3 STRING)
RETURNS STRING
AS (
    CONCAT(LPAD(f1, 2, '0'), '.', LPAD(f2, 2, '0'), '.', LPAD(f3, 8, '0'), '-',
        -- Digito Verificador
        core.fn_aut001_card_digit('0','0', CONCAT('947', LPAD(f1, 2, '0'), LPAD(f2, 2, '0'), LPAD(f3, 8, '0'))))