Sites with hideable announcements/tips

Does anyone know of any site that uses javascript to generate a tip/message/announcement block that has a 'Hide this' option? Pr开发者_如何学编程eferably like Stack Overflow where other containers get shifted up when the tip/announcement is hidden. I'm just trying to compile a list of sites using that feature.

Thanks

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At least Wikipedia uses that kind of announcements with it's fundraising campaigns.