Registry::plugin() 

\nn\t3::Registry()->plugin($vendorName = '', $pluginName = '', $title = '', $icon = '', $tcaGroup = NULL); 

Register a plugin for selection via the dropdown CType in the backend. Use in Configuration/TCA/Overrides/tt_content.php â or ext_tables.php (deprecated).

\nn\t3::Registry()->plugin( 'nncalendar', 'nncalendar', 'Kalender', 'EXT:pfad/zum/icon.svg' );
\nn\t3::Registry()->plugin( 'Nng\Nncalendar', 'nncalendar', 'Kalender', 'EXT:pfad/zum/icon.svg' );

| @return void

public function plugin ( $vendorName = '', $pluginName = '', $title = '', $icon = '', $tcaGroup = null )
{
	\TYPO3\CMS\Extbase\Utility\ExtensionUtility::registerPlugin( $this->getVendorExtensionName($vendorName), $pluginName, $title, $icon, $tcaGroup );
}