diff --git a/classes/cache/CacheFile.class.php b/classes/cache/CacheFile.class.php
index 5540bb8ba..150f634b6 100644
--- a/classes/cache/CacheFile.class.php
+++ b/classes/cache/CacheFile.class.php
@@ -88,7 +88,8 @@ class CacheFile extends CacheBase
 	 * Return whether cache is valid or invalid
 	 *
 	 * @param string $key Cache key
-	 * @param int $modified_time Not used
+	 * @param int $modified_time  	Unix time of data modified.
+	 * 								If stored time is older then modified time, return false.
 	 * @return bool Return true on valid or false on invalid.
 	 */
 	function isValid($key, $modified_time = 0)
@@ -113,7 +114,8 @@ class CacheFile extends CacheBase
 	 * Fetch a stored variable from the cache
 	 *
 	 * @param string $key The $key used to store the value.
-	 * @param int $modified_time Not used
+	 * @param int $modified_time 	Unix time of data modified.
+	 * 								If stored time is older then modified time, return false.
 	 * @return false|mixed Return false on failure. Return the string associated with the $key on success.
 	 */
 	function get($key, $modified_time = 0)