f ( $this->is_external( $url ) ) {
			$errors[] = __( 'You are trying to use an external URL: this is not allowed.', 'sitepress' );

			return false;
		}

		try {
			$response = $wp_http->get( $url );
			if ( is_wp_error( $response ) ) {
				$errors[] = $response->get_error_code() . ' - ' . $response->get_error_message( $response->get_error_code() );

				return false;
			}
			if ( 200 !== (int) $response['response']['code'] ) {
				$errors[] = __( 'An attempt to open the URL specified as a root page failed with the following error:', 'sitepress' );
				$errors[] = $response['response']['code'] . ': ' . $response['response']['message'];

				return false;
			}
		} catch ( Exception $ex ) {
			$errors[] = $ex->getMessage();

			return false;
		}

		return true;
	}

	function is_external( $url ) {
		$site_url        = get_site_url();
		$site_components = wp_parse_url( $site_url );
		$site_host       = strtolower( $site_components['host'] );

		$url_components = wp_parse_url( $url );
		$url_host       = strtolower( $url_components['host'] );

		if ( empty( $url_host ) || 0 === strcasecmp( $url_host, $site_host ) ) {
			return false;
		}

		$site_host = $this->remove_www_prefix( $site_host );

		$subdomain_position = strrpos( $url_host, '.' . $site_host );
		$subdomain_length   = strlen( $url_host ) - strlen( '.' . $site_host );

		return $subdomain_position !== $subdomain_length; // check if the url host is a subdomain
	}

	/**
	 * @param $site_host
	 *
	 * @return string
	 */
	function remove_www_prefix( $site_host ) {
		$site_host_levels = explode( '.', $site_host );
		if ( 2 > count( $site_host_levels ) && 'www' === $site_host_levels[0] ) {
			$site_host_levels = array_slice( $site_host_levels, - ( count( $site_host_levels ) - 1 ) );
			$site_host        = implode( '.', $site_host_levels );
		}

		return $site_host;
	}
}