The ancestorOrigins read-only property of the Location interface is a static DOMStringList containing, in reverse order, the origins of all ancestor browsing contexts of the document associated with the given Location object.
You can use location.ancestorOrigins in the script for a document to determine, for example, whenever the document is being framed by a site which you don't expect it to be framed by. You can also use it to vary the behavior of the document based on what site or list of sites is framing it.