i dont think there is a "regain" but a "region"
its basically for you to allow you to expand/collapse code in between the "markers". The compiler ignores these bookmarks and is only for our readability purposes.
you place your code in between the comments/bookmarks so you can easily navigate or arrange the code. So you can have this code:
string test = String.Empty;
and you can expand or collapse this "node". When collapsed, you can drag this code around instead of having to copy and paste a large chunk of code.