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?

How do you overline text?
[aa][o][/aa]
Is there an order to the tags, or can they all be ordered in anyway, like [aa]'[i][u][b]' , '[b][u][i]' , '[u][b][i]'[/aa] , etc.?
The order you specify is the other that will be used. If there is no visible effect from changing the order, then it doesn't matter what order they are in.
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.
Nested tags.
How do you make the text that has the preceeding |, but the background changes color slightly when you hover over it?
I don't understand what you mean by this? Spoilers? Code tags?

If you need any more help, read shiichan's source code, and more specifically the abbc part.
Use an EXPERT BBCode Viewer to debug your BBCode: http://dis.4chan.org/read/prog/1187966746

To quote use ``> ''  space included.