`val min : char`
`val max : char`
`val is_valid : char -> bool`
`val is_upper : char -> bool`
`val is_lower : char -> bool`
`val is_letter : char -> bool`
`val is_alphanum : char -> bool`
`val is_white : char -> bool`
`val is_blank : char -> bool`
`val is_graphic : char -> bool`
`val is_print : char -> bool`
`val is_control : char -> bool`
`val is_digit : char -> bool`
`val digit_to_int : char -> int`
`val digit_of_int : int -> char`
`val is_hex_digit : char -> bool`
`val hex_digit_to_int : char -> int`
`val lower_hex_digit_of_int : int -> char`
`val upper_hex_digit_of_int : int -> char`
`val uppercase : char -> char`
`val lowercase : char -> char`