Custom TYPO3 form field

ext_localconf.php

<?php

// ...

$GLOBALS['TYPO3_CONF_VARS']['SYS']['formEngine']['nodeRegistry'][1460107841] = [
	'nodeName' => 'tx_tinyurls_urldisplay',
	'priority' => 40,
	'class' => \Tx\Tinyurls\Hooks\UrlDisplayFormElement::class,
];

tx_tinyurls_urls.php

<?php

// TCA config ...

return [
  // ...
  'columns' => [
    // ...
		'urldisplay' => [
			'config' => [
				'type' => 'tx_tinyurls_urldisplay',
			]
		],
		// ...
	],
	'types' => [
		'0' => [
			'showitem' => 'urldisplay...'
		],
	],
];

UrlDisplayFormElement.php

<?php
namespace Tx\Tinyurls\Hooks;


class UrlDisplayFormElement extends \TYPO3\CMS\Backend\Form\AbstractNode implements \TYPO3\CMS\Backend\Form\NodeInterface
{

    /**
     * Main render method
     *
     * @return array As defined in initializeResultArray() of AbstractNode
     */
    public function render()
    {
        $result = $this->initializeResultArray();
        $result['html'] = 'Hallo world!';
        return $result;
    }
}