Funky Caching refers to the generation and display of provisional dynamic content when a solicited resource is not available or has been moved. It is also known as ErrorDocument trick, Smarter Caching and Rasmus' Trick in honor to Rasmus Lerdorf (creator of the PHP programming language), allegedly the first one to present this mechanism (although also attributed to Stig Bakken) in which the HTTP Error404 Error Document is replaced with a script capable of generating dynamic content.
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Funky caching Wikipedia(Text) CC BY-SA