Why can't I set ft_min_word_len? According to the docs, this is available in 4.0. Do I have to use some other syntax?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ mysql> select version(); +-----------+ | version() | +-----------+ | 4.0.12 | +-----------+

mysql> set ft_min_word_len=3; ERROR 1193: Unknown system variable 'ft_min_word_len' ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~