A reference to the parent of the current window or subframe.
If a window does not have a parent, its parent property is a reference to itself.
When a window is loaded in an <iframe>, <object>, or <frame>, its parent is the window with the element embedding the window.
parentWindow = window.parent;
if (window.parent != window.top) {
// we're deeper than one down
} window.frameElement returns the specific element (such as <iframe>) the window is embedded into.window.top returns a reference to the top-level window.
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https://developer.mozilla.org/en-US/docs/Web/API/window/parent