public static function init() {
		self::$integrations = apply_filters(
			'pum_integrations',
			[
				// Forms.
				'ninjaforms'      => new PUM_Integration_Form_NinjaForms(),
				'gravityforms'    => new PUM_Integration_Form_GravityForms(),
				'contactform7'    => new PUM_Integration_Form_ContactForm7(),
				'calderaforms'    => new PUM_Integration_Form_CalderaForms(),
				'mc4wp'           => new PUM_Integration_Form_MC4WP(),
				'wpforms'         => new PUM_Integration_Form_WPForms(),
				'formidableforms' => new PUM_Integration_Form_FormidableForms(),
				// Builders.
				'kingcomposer'    => new PUM_Integration_Builder_KingComposer(),
				'visualcomposer'  => new PUM_Integration_Builder_VisualComposer(),
			]
		);

		self::$preload_posts = isset( $_GET['page'] ) && $_GET['page'] == 'pum-settings';

		add_filter( 'pum_settings_fields', array( __CLASS__, 'settings_fields' ) );
		add_action( 'pum_preload_popup', array( __CLASS__, 'enqueue_assets' ) );
		add_filter( 'pum_registered_conditions', array( __CLASS__, 'register_conditions' ) );

		add_filter( 'pum_vars', array( __CLASS__, 'pum_vars' ) );

		add_action( 'init', array( __CLASS__, 'wp_init_late' ), 99 );
		add_action( 'admin_init', array( __CLASS__, 'admin_init' ) );
		add_filter( 'pum_popup_post_type_args', array( __CLASS__, 'popup_post_type_args' ) );
		add_filter( 'pum_generated_js', array( __CLASS__, 'generated_js' ) );
		add_filter( 'pum_generated_css', array( __CLASS__, 'generated_css' ) );
		add_filter( 'pum_popup_settings', array( __CLASS__, 'popup_settings' ), 10, 2 );

		PUM_Integration_GoogleFonts::init();
	}