pub fn from_digit(num: uint, radix: uint) -> Option<char>
Converts a number to the character representing it.
Returns Some(char) if num represents one digit under radix,
using one character of 0-9 or a-z, or None if it doesn't.
Fails if given an radix > 36.
Prefix searches with a type followed by a colon (e.g.
fn:) to restrict the search to a given type.
Accepted types are: fn, mod,
struct (or str), enum,
trait, typedef (or
tdef).