Writeups from challenges and CTFs i take part in.
What you have to do:
Inject the following JavaScript command: alert(document.domain);
Hint:
This stage is not currently available, not even through the wayback machine. I got the next level by looking for an URL online.
A possible solution is
"><a href="javascr ipt:alert(document.domain);">XSS</a>
as explained here.