How to make sure tooltip content is indexed by Google? (Rap lyrics-related)

On Rap Exegesis, you can click lyrics to see them explained in a tooltip:

alt text http://img405.imageshack.us/img405/3577/20091027114851.png

These explanations are stored in hidden <div>s that are included in the page. (Firebug the page linked above to see what I mean)

My question is how to make sure these explanations are indexed by Google, since by default Google doesn't index invisible content (right?).

One option would be to, instead of sett开发者_StackOverflowing display: none on these divs, absolutely position them, say, left: -9999em. This approach might have other downsides though.

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It's not invisible to a crawler that has no eyes.

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Content such as what you see above is not hidden to Google - as long as it is included somewhere within the page's HTML code (i.e. AJAX loaded content from an external file will not be indexed).

To see exactly what Google sees when it indexes content on your website, utilize Google's Webmaster Tools - Fetch As Google.