form_validator.erl

%% @type predicate() = {'duplication', [field()]} |
%%                     'not_empty' |
%%                     'string' |
%%                     {'length', [Exact::integer()]} |
%%                     {'length', [Min::integer(), Max::integer()]} |
%%                     {'predicate', function()} |
%%                     {'not_predicate', function()} |
%%                     'email_address' |
%%                     {'regex', Regex::string()} |
%%                     {'member', [term()]}.