Function nom::hex_digit

pub fn hex_digit<T>(input: T) -> IResult<T, T> where
    T: Slice<Range<usize>> + Slice<RangeFrom<usize>> + Slice<RangeTo<usize>>,
    T: InputIter + InputLength,
    <T as InputIter>::Item: AsChar, 

Recognizes one or more hexadecimal numerical characters: 0-9, A-F, a-f