Extend backend form in OctoberCMS

Plugin.php

<?php

public function boot()
{
	// Extend all backend form usage
	Event::listen('backend.form.extendFields', function($widget) {

		// Only for the Posts controller
		if (!$widget->getController() instanceof \RainLab\Blog\Controllers\Posts)
			return;

		// Only for the Post model
		if (!$widget->model instanceof \RainLab\Blog\Models\Post)
			return;

		// Update content field
		$widget->addSecondaryTabFields([
			'content' => [
				'tab' => 'rainlab.blog::lang.post.tab_edit',
				'type' => 'richeditor',
				'size' => 'huge',
			]
		]);
	});

}