Make it clear and the beginning of the overlay description that this...

Make it clear and the beginning of the overlay description that this constraint only applies to add and modify commands via a modify request.

doc/man/man5/slapo-constraint.5

@@ -16,6 +16,9 @@ when modifying an attribute value under constraint.
 This overlay is intended to be used to force syntactic regularity upon
 certain string represented data which have well known canonical forms,
 like telephone numbers, post codes, FQDNs, etc.
+.LP
+It constrains only LDAP adds and modify commands and only seeks to
+control the add and modify value of a modify request.
 .SH CONFIGURATION
 This
 .B slapd.conf