Function width_elems 

pub(crate) fn width_elems(
    access: &TokenStream,
    borrowed: bool,
    elem_ty: &Type,
    iter: &Ident,
    elems: &[Ident],
) -> TokenStream

Bind the first elems.len() elements of a width = N field value access to Option<T> variables (None past its end; elements past N are dropped), through iterator variable iter.