diff --git a/doc/config/conf.d/ssi.conf b/doc/config/conf.d/ssi.conf
index cd1f552c..6b78f5c9 100644
--- a/doc/config/conf.d/ssi.conf
+++ b/doc/config/conf.d/ssi.conf
@@ -39,6 +39,10 @@ ssi.extension              = ( ".shtml" )
 ##
 ## Disabled by default.
 ##
+## For further explanation of conditional requests, please see
+## Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests
+## https://tools.ietf.org/html/rfc7232
+##
 #ssi.conditional-requests = "enable"
 
 ##