It is nice to meet everybody in this forum.
Last night, I found a very interesting topic
http://msdn.microsoft.com/en-us/library/aa479051.aspx . Content of this topic teach you how to create a customize asp.net control.
And at this section of this topic
http://msdn.microsoft.com/en-us/library/aa479051.aspx#cccdesign_topic7 the author also tells you about clicking event handling (sound like you click an element at design region control). However, how can I create a event handling to popup other control
in design screen mode?
I create a demonstration for my idea :
First step (click an elment at the region hightlight)
Second step (show a popup control)
Go to the complete details ...