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"Facebook today announced new custom audience features that let advertisers and market target users who have previously visited their website and or used their mobile app. The new tools ..."^^<http://www.w3.org/2001/XMLSchema#string>
<http://thenextweb.com/facebook/2013/10/15/facebook-announces-tools-let-advertisers-target-people-visited-site-used-mobile-app/>