my @a = qw[a simple list];
    Internals::SvREADONLY(@a,    1);
    Internals::SvREADONLY($a[1], 1); # Make our target element RO (double sure!)
    warn '$a[1] is ' . (Internals::SvREADONLY($a[1]) ? '' : 'not ') . 'read-only';
    warn join ' ', @a;               
    eval { $a[1] = 'changed' };      # Modification of a read-only value attempted
    warn join ' ', @a;               
    splice(@a, 1, 1, 'spliced');
    warn join ' ', @a;               
    warn '$a[1] is ' . (Internals::SvREADONLY($a[1]) ? '' : 'not ') . 'read-only';