ext_tables.php

<?php
if (!defined('TYPO3_MODE')) {
	die ('Access denied.');
}

// Registering as Plugin
\TYPO3\CMS\Extbase\Utility\ExtensionUtility::registerPlugin(
	'Ipf.' . $_EXTKEY,
	'pi1',
	'issuu'
);

\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addStaticFile($_EXTKEY, 'Configuration/TypoScript', 'issuu');

// Flexform stuff
$extensionName = \TYPO3\CMS\Core\Utility\GeneralUtility::underscoredToUpperCamelCase($_EXTKEY);
$pluginSignature = strtolower($extensionName) . '_pi1';

$GLOBALS['TCA']['tt_content']['types']['list']['subtypes_excludelist'][$pluginSignature] = 'layout,select_key,recursive';
$GLOBALS['TCA']['tt_content']['types']['list']['subtypes_addlist'][$pluginSignature] = 'pi_flexform';
\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addPiFlexFormValue($pluginSignature, 'FILE:EXT:' . $_EXTKEY . '/Configuration/Flexform/flexform_ds_pi1.xml');

?>