Should the parent window be able to navigate the popup window, even if it's cross origin? If not, now you're suggesting some sort of asymmetric security checks

Should the parent window be able to navigate the popup window, even if it's cross origin? If not, now you're suggesting some sort of asymmetric security checks that depend on something that's not just the origins. Security checks that, chances are, will be easy to evade by malicious actors. At least I haven't thought of a non-evadable one here yet.