What is the <i> tag use for?

Well I know it is meant to italicize text, but I have been using firebug on Facebook and I cannot help but realize how much they use the <i> tags in their layout.

For example, for the photo thumbnail gallery, Facebook uses the <i> tag inside a div and places a ba开发者_C百科ckground image style for the tag in the photo gallery. Are there more tricks/tips/uses to the tag ?

The i element has not been deprecated (contrary to popular belief), but its use to strictly italicize text has been.

The i element represents a span of text in an alternate voice or mood, or otherwise offset from the normal prose, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, a thought, a ship name, or some other prose whose typical typographic presentation is italicized

Source.

The last time I personally used it was to markup the scientific names of plants, eg...

<i>Anredera cordifolia</i> (Madiera Vine) 

Update

The reason Facebook may use it is because they deal with millions of concurrent requests - sending i down instead of span saves some bytes. Using it also doesn't suffer in readability too bad, as opposed to changing that class from tagWrapper to a.

If you want to see byte saving to the extreme, look at Google's home page source.

See Wikipedia's Manual of Style. Granted, it is not the universal manual of style, but it does give you an idea of what italics are used for, and how it is different from emphasis <em>. While the former is used for certain special names, referring to a name as introduction, or for foreign phrases, the latter is strictly for emphasis.

As for uses outside the above mentioned, it probably is just another of those tag misuses.