When to use window.opener / window.parent / window.top

• window.opener refers to the window that called window.open( ... ) to open the window from which it's called
• window.parent refers to the parent of a window in a <frame> or <iframe> or popups which are opened by using window.open()
• window.top refers to the top-most window from a window nested in one or more layers of <iframe> sub-windows

Thanks,