The "Online Help" files in the wiki are still very much under construction, but you should still check here: http://www.saas.nsw.edu.au/koha_wiki/index.php?page=SubFields for some helpful information. Stephen Eric G. Salayon said:

in modifying tags (MARC tag structures), what is meant by Repeatable, Mandatory and Authorised value? i assumed that authorised value are derived from data in the system parameter, am i correct?

-- Stephen Hedges Skemotah Solutions, USA www.skemotah.com -- shedges@skemotah.com