Nette\Forms\Form::setRenderer PHP Method

    public function setRenderer(IFormRenderer $renderer = NULL)
    {
        $this->renderer = $renderer;
        return $this;
    }

<?php

// Latte: {$Forms[contact]}
use Nette\Forms\Form;
$form = new Form();
$form->setRenderer(new \Nextras\Forms\Rendering\Bs3FormRenderer());
$form->addProtection('Detected robot activity.');
$c = $form->addContainer('frm');
$c->addText('email', 'Your email')->addCondition($form::FILLED)->addRule($form::EMAIL, 'Please fill in a valid e-mail address.');
$c->addTextarea('message', 'Message')->setRequired('Please fill in a message.');
$c->addSubmit('send', 'Send');
if (isFormValid($form, __FILE__)) {
    dump($c->getValues());
}
return $form;