This is like setResponseExpires, but it can be called multiple times. The setting most in the past is the one kept. If you have multiple functions, they all might call updateResponseExpires about their own return value. The program output as a whole is as cacheable as the least cachable part in the chain. setCache(false) always overrides this - it is, by definition, the strictest anti-cache statement available. If your site outputs sensitive user data, you should probably call setCache(false) when you do, to ensure no other functions will cache the content, as it may be a privacy risk. Conversely, setting here overrides setCache(true), since any expiration date is in the past of infinity.