A kept listing and whether it is current, or null when none is kept.
Optionalcache_Forgets one folder's listing: something in it changed.
Optionalcache_Forgets a folder's listing and every one beneath it: the folder went.
Keeps a listing; with since, only when nothing invalidated its folder after that stamp.
Optionaloptions: { since?: number }Optionalstamp_A stamp to take before fetching a listing, handed back to cache_set as since.
A listing cache: listings kept for a while, each saying whether it is still current.