Explicitly setting timer's 'active' field to '1' after user changes

FORMATS

@@ -41,7 +41,10 @@ Video Disk Recorder File Formats
   The fields in a timer definition have the following meaning (from left
   to right):
 
-  - Timer active (0 = inaactive, 1 = active)
+  - Timer active (0 = inactive, 1 = active)
+    Values larger than '1' can be used by external programs to mark active timers
+    and recognize if the user has modified them. When a user modifes an active
+    timer the 'active' field will be explicitly set to '1'.
   - Program number of the channel to record
   - Day of recording, either one or more of
       M------ = Monday