public function add_validation_rule(callable $callback) {
        if ($this->mode == self::MODE_COMPLETE) {
            $this->_form->addFormRule($callback);
        }
    }
public function add_validation_rule(callable $callback) {
        if ($this->mode == self::MODE_COMPLETE) {
            $this->_form->addFormRule($callback);
        }
    }
public function add_validation_rule ( callable $ callback ) { if ( $ this -> mode == self :: MODE_COMPLETE ) { $ this -> _form -> addFormRule ( $ callback ) ; } }
Adds a validation rule to the form

@param callable $callback with arguments ($values, $files)
Adds a validation rule to the form