Add clarifying docs

functions/abook_database.php

@@ -295,6 +295,10 @@ class abook_database extends addressbook_backend {
      *                       of the SM_ABOOK_FIELD_* constants
      *                       defined in include/constants.php
      *                       (OPTIONAL; defaults to nickname field)
+     *                       NOTE: uniqueness is only guaranteed
+     *                       when the nickname field is used here;
+     *                       otherwise, the first matching address
+     *                       is returned.
      *
      * @return array Array with lookup results when the value
      *               was found, an empty array if the value was

functions/abook_ldap_server.php

@@ -729,6 +729,10 @@ class abook_ldap_server extends addressbook_backend {
      *                       of the SM_ABOOK_FIELD_* constants
      *                       defined in include/constants.php
      *                       (OPTIONAL; defaults to nickname field)
+     *                       NOTE: uniqueness is only guaranteed
+     *                       when the nickname field is used here;
+     *                       otherwise, the first matching address
+     *                       is returned.
      *
      * @return array Array with lookup results when the value
      *               was found, an empty array if the value was

functions/abook_local_file.php

@@ -324,6 +324,10 @@ class abook_local_file extends addressbook_backend {
      *                       of the SM_ABOOK_FIELD_* constants
      *                       defined in include/constants.php
      *                       (OPTIONAL; defaults to nickname field)
+     *                       NOTE: uniqueness is only guaranteed
+     *                       when the nickname field is used here;
+     *                       otherwise, the first matching address
+     *                       is returned.
      *
      * @return array Array with lookup results when the value
      *               was found, an empty array if the value was

functions/addressbook.php

@@ -606,6 +606,10 @@ class AddressBook {
      *                       of the SM_ABOOK_FIELD_* constants
      *                       defined in include/constants.php
      *                       (OPTIONAL; defaults to nickname field)
+     *                       NOTE: uniqueness is only guaranteed
+     *                       when the nickname field is used here;
+     *                       otherwise, the first matching address
+     *                       is returned.
      *
      * @return mixed Array with lookup results when the value
      *               was found, an empty array if the value was
@@ -929,6 +933,10 @@ class addressbook_backend {
      * @param integer $field The field to look in, should be one
      *                       of the SM_ABOOK_FIELD_* constants
      *                       defined in include/constants.php
+     *                       NOTE: uniqueness is only guaranteed
+     *                       when the nickname field is used here;
+     *                       otherwise, the first matching address
+     *                       is returned.
      *
      * @return mixed Array with lookup results when the value
      *               was found, an empty array if the value was