e.event.stopImmediatePropagation() will use the native sIP if available.
AFAIK, there's no built-in MooTools support for (creating and) stopping a userland event chain on the same element; that is how jQ allows access to sIP even if the browser doesn't support it. Somebody might have written such a class... you certainly could! But what's the exact use case here? -- S.
