Explaining the BBcode?

I don't quite think lurk moar would cover this, considering the BBcodes are interpreted and then we only see their output. I understand [u], [i], [b], [spoiler], and [code]. I've seen, but I don't know if [sup] and [sub] work. I have just a few questions.
How do you overline text?
Is there an order to the tags, or can they all be ordered in anyway, like '[i][u][b]' , '[b][u][i]' , '[u][b][i]' , etc.?
To do multilayered spoilers do you simply layer the tag? I saw this one spoilered text that was A-Z and if you highlighted A, it was only A, and B was both A and B, and highlighting Z showed the whole text.
How do you make the text that has the preceeding |, but the background changes color slightly when you hover over it?

>>147
I think people have a chance of figuring it out on their own.
I knew how to quote, but I had no idea how to multiline quote, or do the fancy quotes other people do. Some anon laughed at me for not doing multi-line quoting properly, and I picked some random ancient thread, and in some 30-40 posts of experiementing, I had figured out probably everything there is to know about multi-line quoting and changing levels of quoting.

Good luck to anons out there, and remember to use sage when posting, or just install your local copy of Shiichan and read the source code!