Source

File: wp-admin/includes/misc.php

function show_message( $message ) {
	if ( is_wp_error( $message ) ) {
		if ( $message->get_error_data() && is_string( $message->get_error_data() ) ) {
			$message = $message->get_error_message() . ': ' . $message->get_error_data();
		} else {
			$message = $message->get_error_message();
		}
	}
	echo "<p>$message</p>\n";
	wp_ob_end_flush_all();
	flush();
}