nginx hack for multiple conditions

nginx.conf

    if ($request_uri = /) { 
      set $test  A; 
    } 
  
    if ($host ~* teambox.com) { 
      set $test  "${test}B"; 
    } 
  
    if ($http_cookie !~* "auth_token") { 
      set $test  "${test}C"; 
    } 
    
    if ($test = ABC) { 
      proxy_pass http://teambox-cms.heroku.com; 
      break; 
    } 

this is awesome!

Need explanation.... what actually this does:
if ($host ~* teambox.com) {
set $test "${test}+teambox.com";
}
Does it takes "this".teambox.com or what? Thanks!

How to write this condition?

if ($host *.teambox.com) {
set $subdomain_name = ?;
}

Thanks!

Awesome!!!! Thanks!
If somebody needs an explanation what the code does is it sequentially appends different letters to one variable.
When all the letters are present that means that all the required conditions have been met.