Made getWithSetCallback doc comment clearer

Change-Id: I68c3929691c886bcfee32499a6058f01f69ea63c

diff --git a/includes/libs/objectcache/WANObjectCache.php b/includes/libs/objectcache/WANObjectCache.php
index 0437fad..7f55456 100755 (executable)
--- a/includes/libs/objectcache/WANObjectCache.php
+++ b/includes/libs/objectcache/WANObjectCache.php
@@ -305,11 +305,14 @@ class WANObjectCache {
         * 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: