when will the "realize"&"unrealize" signals be emitted?

[Randy <randyqiuxy hotmail com>]

Hi list,
I know a widget will realized,mapped and visible before it appears on
the screen.Then,
1)
But who can tell me what it actually does during the three periods?
2)
when the "unrealize" signal emission happens? And what the correspond
callback does?
Thanks a lot!

Best regards,
Randy