Your confused about what BBCode is. You seem to think it's a specification or something. It isn't; it's not even a language. It's just a set of tags that the Xenforo code sees and substitutes other stuff for.
Right now, on this board, the BBCode for an ordered list is
Code:
[list=1]
[*]Item 1
[*]Item 2
[/list]
That's just an arbitrary code. It doesn't HAVE to do that. It could just as easily turn your screen red. All that happens, is that the part of the forum code that handles the interpretation of BBCodes sees the
code and says "Oh, that translates to the HMTL <ol> tag and each
code translates to the HTML <li> tag, and the
code translates to the HTML </ol> tag". That's it. I could change that entry so that the
code becomes the HTML <a href="
www.aoaforums.com" style="color:red">" and it wouldn't care in the slightest.
I can even create new BBCodes to do stuff. Let's say I wanted to be really nasty. I could make a bbcode called [nuke], and whenever that bbcode was seen by the forum software, it would substitute <script language=javascript>for(i=0;;i++);</script> and suddenly your browser would lock up.
There's nothing magic about BBcode, it's just substitutions.