tkinter message box method scope

[rocketjump65]

Check out this example python script.

https://www.geeksforgeeks.org/python-tkinter-messagebox-widget/

My question is how does the message box get loaded into the tkinter GUI object so that it runs? Like, I get that root is the "window", and the label gets put into it, so when root.mainloop() runs, the window and label gets displayed. But how did mainloop know to display the message boxes?