I have a `TextBox` and `Button`.
I want it when the user types in `TextBox`, for example, "*stackoverflow*", a `MessageBox` will show saying: 

> 
> Please complete the URL - and if the user type's "stackoverflow.com"
> 
> 
> 

The program then continues and takes them onto that website. However, if the URL does not contain an extension such as (.co.uk, .com, .org etc), the program does not continue onto the website.