prettyPhoto is a jQuery based lightbox clone. Not only does it support images, it also add support for videos, flash, YouTube, iFrames. It’s a full blown media lightbox. The setup is easy and quick, plus the script is compatible in every major browser.
Adding a rel attribute such as "prettyPhoto[folio]" breaks validation results and therefore is not compatible to the standard.
See results of a HTML5 page over at: http://validator.w3.org/