Changes have been made in Git for this ticket:

Bug #9087: Fix prefs documentation

http://git.horde.org/diff.php/imp/config/prefs.php.dist?rt=horde-git&r1=5504e4168d051107a90b357195977e5cf1bb865a&r2=e0b94d1c9d08ff8a0d94ba0aa507b33c3858244a
http://git.horde.org/diff.php/kronolith/config/prefs.php.dist?rt=horde-git&r1=4343b7a9079e436ff77770deb9adb6b1f38cc29c&r2=e0b94d1c9d08ff8a0d94ba0aa507b33c3858244a
http://git.horde.org/diff.php/turba/config/prefs.php.dist?rt=horde-git&r1=2b3abe74f295dcedc13498a2c86131c493977d4b&r2=e0b94d1c9d08ff8a0d94ba0aa507b33c3858244a
http://git.horde.org/diff.php/whups/config/prefs.php.dist?rt=horde-git&r1=686d5ca6ac47356af4ec4620486adff71baecdce&r2=e0b94d1c9d08ff8a0d94ba0aa507b33c3858244a

// Address book(s) to use when expanding addresses
// Refer to turba/config/sources.php for possible source values
//
// You can provide default values this way:
//   'value' => json_encode('source_one', 'source_two')

It should be
//   'value' => json_encode(array('source_one', 'source_two'))


Same error with :
- turba : $_prefs['addressbooks']
- kronolith : $_prefs['search_sources']
- whups : $_prefs['search_sources']