WP_Theme::get_allowed

		 * be filtered further.
		 *
		 * @since 4.5.0
		 *
		 * @param string[] $allowed_themes An array of theme stylesheet names.
		 * @param int      $blog_id        ID of the site.
		 */
		$network = (array) apply_filters( 'network_allowed_themes', self::get_allowed_on_network(), $blog_id );
		return $network + self::get_allowed_on_site( $blog_id );
	}

	/**
	 * Returns array of stylesheet names of themes allowed on the network.
	 *
	 * @since 3.4.0