diff --git a/doc/configuration.txt b/doc/configuration.txt
index b2c25d4..eea9563 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -11312,6 +11312,11 @@
       incremented. Most of the time it will be used to measure the frequency of
       occurrence of certain events (e.g. requests to a specific URL).
 
+    - gpt0 : first General Purpose Tag. It is a positive 32-bit integer
+      integer which may be used for anything. Most of the time it will be used
+      to put a special tag on some entries, for instance to note that a
+      specific behavior was detected and must be known for future matches
+
     - conn_cnt : Connection Count. It is a positive 32-bit integer which counts
       the absolute number of connections received from clients which matched
       this entry. It does not mean the connections were accepted, just that