docs: |
    Trivially implemented as:
     
        my $pos    = index( lc $haystack, lc $needle );
        my $second = index( lc $haystack, lc $needle, $pos );

    Note that unlike C<stripos>, C<index> returns C<-1> if
    C<$needle> is not found. This makes testing much simpler.

    If you want the additional behaviour of non-strings being
    converted to integers and from there to characters of
    that value, then you're silly. If you want to find a
    character of particular value, explicitly use the
    C<< L<chr|perlfunc/"chr"> >> function:

        my $charpos = index( lc $haystack, lc chr $char );