What exactly is controlled by the Manual:$wgCachePages configuration setting? Manual page is very minimal.
Topic on Project:Support desk
I have expanded the page a little.
THe code is at https://github.com/wikimedia/mediawiki/blob/d6dcf23a8f22245e311d5582e4f9cd0f302e3738/includes/AjaxResponse.php#L223, so if you want to have a look yourself, you also can do that.