Function first_range_begin_end 

pub fn first_range_begin_end<T, V, C: IncDecCpCmp<T, V>, R: GetBeginEnd<T>>(
    src: &[R],
    step: &V,
    t: &C,
) -> Option<(T, T)>

Looks for the first most range, if found returns an Option<(T,T)>.