The self property returns the current window.
The self property is supported in all major browsers.
When the "Check window" button is clicked, the function check() is called and the current window status is checked. If the topmost window (window.top) is different from the current window (window.self), then output that "This window is not the topmost window! Am I in a frame?". If the topmost window equals the current window, then fire the else statement:
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