[2perfect]

I've mostly been using the <b> and <i> tags for web designing, but when I came across <strong> and <em> a while back, I started using those 2 tags instead. Then a month ago I figured out that I can also use <span> to reach the same effect with font-weight:bold and font-style:italic.

So I was just wondering, if they all produce the same effect, what's the difference? Which is best to use, and why?

The only difference I have found so far is that <em> doesn't necessarily italicize, but emphasizes, and <strong> doesn't necessarily boldfaces, but strengthens(?). Although every time I use them, I get the italicized and boldfaced effect.