clarify that replacement, but not expression evaluation,

is done on the string in group.regex=string
We really should rename the style, in this case, to "replacement".

doc/man/man5/slapd.access.5

@@ -240,7 +240,8 @@ can be
 .BR regex ,
 which means that
 .B <group>
-will be expanded according to regex (7), and
+will be expanded as a replacement string (but not as a regular expression)
+according to regex (7), and
 .B base
 or
 .B exact