JavaScript sandboxing is a sort of orthogonal concern to what Cowl is after. Cowl needs sandboxing to work (either by built-in browser support, or by Caja et al

JavaScript sandboxing is a sort of orthogonal concern to what Cowl is after. Cowl needs sandboxing to work (either by built-in browser support, or by Caja et al), but even with a sandbox, you still need some sort of policy for when to allow data in and out of the scripts, and that's one of the main things Cowl provides.