diff --git a/doc/configuration.txt b/doc/configuration.txt
index 53d1b0b..8ee6438 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -15708,7 +15708,11 @@
 All ACL-specific criteria imply a default matching method. Most often, these
 criteria are composed by concatenating the name of the original sample fetch
 method and the matching method. For example, "hdr_beg" applies the "beg" match
-to samples retrieved using the "hdr" fetch method. Since all ACL-specific
+to samples retrieved using the "hdr" fetch method. This matching method is only
+usable when the keyword is used alone, without any converter. In case any such
+converter were to be applied after such an ACL keyword, the default matching
+method from the ACL keyword is simply ignored since what will matter for the
+matching is the output type of the last converter. Since all ACL-specific
 criteria rely on a sample fetch method, it is always possible instead to use
 the original sample fetch method and the explicit matching method using "-m".