How It Works
In step 4 of this exercise you set the Visible property of the Panel control to False. This means that when the page loads, the control is not visible on the server and thus its HTML never makes it to the browser. When you then check the check box, a post back occurs, which sends the information contained in the form to the server. At the server, some code is run that is fi red whenever the check box changes its state from checked to unchecked or vice versa. Inside that code block, the following code is executed (shown in C#):