Can methods taking AnyObject be safe?

[madsmtm]

Methods like NSAccessibilityElement::accessibilityElementWithRole_frame_label_parent or NSResponder::insertTab take &AnyObject.
This means that they can assume very little about the object, but that's usually fine, as it's only really used in user-implemented methods (I think?).

Can we allow such methods to be safe? What about if I were to pass a &NSMutableString? Would that still be safe because I/the method can't recover the mutable string, or would safety be broken here?

---

Related is methods like NSError::initWithDomain_code_userInfo or NSAttributedString::initWithString_attributes, which accept NSDictionary<SomeKey, AnyObject>, and expect the user to pass the correct type for a given key.
Does Foundation assert that the attributes are the correct type? If so, can we allow these methods to be safe?