public function add_model($class, $instance = null, $method = 'set_form_fields')
	{
		// Add model to validation callables for validation rules
		$this->validation()->add_callable($class);

		if ((is_string($class) and is_callable($callback = array('\\'.$class, $method)))
			|| is_callable($callback = array($class, $method)))
		{
			$instance ? call_user_func($callback, $this, $instance) : call_user_func($callback, $this);
		}

		return $this;
	}