add_settings_error()函数是Wordpress函数，注册要显示给用户的设置错误。

add_settings_error( string $setting, string $code, string $message, string $type = ‘error’ )

注册要显示给用户的设置错误。
Register a settings error to be displayed to the user.

说明（Description）

设置API的一部分。使用此选项可向用户显示有关设置验证问题、缺少设置或其他任何内容的消息。

应在给定设置的register_setting（）中定义的$sanitize_回调函数中添加设置错误，以提供有关提交的反馈。

默认情况下，消息将在生成错误的提交后立即显示。对settings_errors（）的其他调用可用于显示错误，即使首次访问设置页也是如此。

参数（Parameters）

返回（Return）

无返回值

源码（Source）

/**
 * Register a settings error to be displayed to the user
 *
 * Part of the Settings API. Use this to show messages to users about settings validation
 * problems, missing settings or anything else.
 *
 * Settings errors should be added inside the $sanitize_callback function defined in
 * register_setting() for a given setting to give feedback about the submission.
 *
 * By default messages will show immediately after the submission that generated the error.
 * Additional calls to settings_errors() can be used to show errors even when the settings
 * page is first accessed.
 *
 * @since 3.0.0
 *
 * @global array $wp_settings_errors Storage array of errors registered during this pageload
 *
 * @param string $setting Slug title of the setting to which this error applies
 * @param string $code    Slug-name to identify the error. Used as part of 'id' attribute in HTML output.
 * @param string $message The formatted message text to display to the user (will be shown inside styled
 *                        `` and `` tags).
 * @param string $type    Optional. Message type, controls HTML class. Accepts 'error' or 'updated'.
 *                        Default 'error'.
 */
function add_settings_error( $setting, $code, $message, $type = 'error' ) {
	global $wp_settings_errors;
	$wp_settings_errors[] = array(
		'setting' => $setting,
		'code'    => $code,
		'message' => $message,
		'type'    => $type
	);
}

笔记（Notes）

基本示例