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?

i'm feeling generous, so i'll post this:

[b] bold
[u] underline
[o] underline
[i] italic
[s] strikethrough
[m] couriour text
[#] ignores all bbcode tags inside it
[rem] hides text inside the tag
[code] preserves syntax for code and colors text
[spoiler] for spoilers
[sup] makes text progressivly smaller higher on the line
[sub] makes text progressivly smaller lower on the line
[aa] For SJIS art.
For ASCII art use [m] tag.
To quote put "> " on a new line, ignore the quotes but do keep the space everything typed on that line will be quoted
To multiquote put "> " before the first line end the line with [o] then put "> > "before the next line of text, again ending with [o] third line: "> > > " then end with [o] then on another new line close the three [o] tags.