* value (false if not present). If false is returned, then nothing
* will be saved to cache.
*
- * Most callers should ignore the current value, but it can be used
+ * Usually, callbacks ignore the current value, but it can be used
* to maintain "most recent X" values that come from time or sequence
* based source data, provided that the "as of" id/time is tracked.
*
- * Usage of $checkKeys is the same as with get().
+ * Usage of $checkKeys is similar to get()/getMulti(). However,
+ * rather than the caller having to inspect a "current time left"
+ * variable (e.g. $curTTL, $curTTLs), a cache regeneration will be
+ * triggered using the callback.
*
* The simplest way to avoid stampedes for hot keys is to use
* the 'lockTSE' option in $opts. If cache purges are needed, also: