Board Thread:The Time Lord Academy/@comment-24451551-20150803183720/@comment-1432718-20150804043657

Both Tardis:Citation and Tardis:What does a citation mean? show examples of how we require in-universe citations to be done, and that is with a period before the citation in parentheses. Now that doesn't answer your question of why we do it this way.

If a reason has ever been given (and my sometimes faulty memory tells me that I have seen it somewhere on this wiki), it would be rather hard to find. However, I do know that in the early days of this wiki, the admins and other users often took the Star Trek wiki as an example. From what I can tell, they cite their stories the way we do.