I'm not sure if code comments are part of "Documentation", but I didn't see a more likely category.
from includes/DefaultSettings.php :
- This will cache static pages for non-logged-in users to reduce
- database traffic on public sites.
- Must set $wgShowIPinHeader = false
- ResourceLoader requests to default language and skins are cached
- as well as single module requests. */
$wgUseFileCache = false;
The comment about "Must set wgShowIPinHeader = false" has not been true for some time, as it is done automatically when File Cache is used (since 1.15 according to HISTORY).