code: function(field, rule) {
              var
                $field       = module.get.field(field.identifier),
                type         = rule.type,
                value        = $field.val(),
                isValid      = true,
                ancillary    = module.get.ancillaryValue(rule),
                ruleName     = module.get.ruleName(rule),
                ruleFunction = settings.rules[ruleName]
              ;
              if( !$.isFunction(ruleFunction) ) {
                module.error(error.noRule, ruleName);
                return;
              }
              // cast to string avoiding encoding special values
              value = (value === undefined || value === '' || value === null)
                ? ''
                : $.trim(value + '')
              ;
              return ruleFunction.call($field, value, ancillary);
            }
docs: takes validation rule and returns whether field passes rule