diff --git a/_.htaccess b/_.htaccess
index c1198a198efd3aade284f5d7fe79a224764ae4bf..910a643c3c11ae93508ac56c9fd972442247d8a6 100644
--- a/_.htaccess
+++ b/_.htaccess
@@ -50,7 +50,15 @@
 		</IfModule>
 	</IfModule>
 
-	# Compress all output labeled with one of the following media types
+	# Compress all output labeled with one of the following media types.
+	#
+	# (!) For Apache versions below version 2.3.7 you don't need to
+	# enable `mod_filter` and can remove the `<IfModule mod_filter.c>`
+	# and `</IfModule>` lines as `AddOutputFilterByType` is still in
+	# the core directives.
+	#
+	# https://httpd.apache.org/docs/current/mod/mod_filter.html#addoutputfilterbytype
+
 	<IfModule mod_filter.c>
 		AddOutputFilterByType DEFLATE application/atom+xml \
 			application/javascript \