diff --git a/doc/reference.conf b/doc/reference.conf
index 54a07358..9d6bdf4a 100644
--- a/doc/reference.conf
+++ b/doc/reference.conf
@@ -26,6 +26,10 @@
  *        .include "filename"
  *        .include <filename>
  *
+ * Flags variables are comma-separated sets of predefined values,
+ * specific to each block. For example in operator {} blocks:
+ *        flags = encrypted, encrypted;
+ *
  * Times/durations are written as:
  *        12 hours 30 minutes 1 second
  *