Function submatch_ignore_ascii_case 

pub fn submatch_ignore_ascii_case<T1, T2>(s: T1, sub: T2) -> bool
where
    T1: AsRef<[u8]>,
    T2: AsRef<[u8]>,

Returns true if sub occurs within s, using ASCII case insensitive comparison.

This is a convenience wrapper around contains_ignore_ascii_case.