Why doesn't clicking on a child element propagate to the parent?

```
from tkinter import *

root = Tk()

def handler(event):
    print('clicked at', event.x, event.y)

frame = Frame(root, width=100, height=100)
label = Label(frame, text="Label")
frame.bind('<Button-1>', handler)
frame.pack()
label.pack(side=TOP)

root.mainloop()

```

When I run that, clicking on the label doesn't fire the handler. I've understood that events propagate to parents by default and if you didn't want that, you'd have to return "break"