Citation:
Alexey Feldgendler from Opera kindly alerted us to the possibility that certain non-browser environments (like Opera’s widget system) do not enforce the same-origin policy and as such may be subject to cross-domain script exploits.
To combat this we’ve added an Ajax.Request#isSameOrigin method which returns true when a request is being made to the same domain, port, and protocol as the document.
Furthermore, Prototype will no longer automatically evaulate JavaScript response bodies when this method returns false.
et en regardant le code de Ajax.Request#isSameOrigin de plus près, c'est confirmé. Prototype n'evalue plus la réponse, même si elle est fournie par le serveur.