--- doc/autoconf.texi
+++ doc/autoconf.texi
@@ -5006,7 +5006,10 @@
 Check for the existence of each @address@hidden@var{member}} of
 @var{members} using the previous macro.  When @var{member} belongs to
 @var{aggregate}, define @address@hidden@var{member}} (in all
-capitals, with spaces and dots replaced by underscores).
+capitals, with spaces and dots replaced by underscores).  If
address@hidden is given, it is executed for each of the found
+members.  If @var{action-if-not-found} is given, it is executed for each
+of the members that could not be found.
 
 This macro uses m4 lists:
 @example