page — such as the text you typed in the text box — is sent back to the server. ASP.NET reacts to the
postback by rendering the page again. However, this time it prepopulates controls, like the TextBox,
with the values that were sent to the page.
Take a look at the resulting HTML for the page after the postback, using the browser’s View Source
command (rerun the page from VS by pressing Ctrl+F5 if you already closed it). You should see code
similar to this: