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function is not described

wp_password_change_notification() WP 2.7.0

Notify the blog admin of a user changing password, normally via email.

This is a pluggable function, and it can be replaced from plugin. It means that this function is defined (works) only after all plugins are connected (included), but before this moment the function has not yet been defined... Therefore, you cannot call this and all functions depended on this function directly from a plugin code. It must be called via hook plugins_loaded or later, for example on hook init.

Function replacement (override) — in a plugin you can create a function with the same name, then it will replace this function.

Hooks in function
Return

Nothing (null).

Usage

wp_password_change_notification( $user );
$user(WP_User) (required)
User object.

Code of wp password change notification: wp-includes/pluggable.php VER 5.0.3

<?php
function wp_password_change_notification( $user ) {
	// send a copy of password change notification to the admin
	// but check to see if it's the admin whose password we're changing, and skip this
	if ( 0 !== strcasecmp( $user->user_email, get_option( 'admin_email' ) ) ) {
		/* translators: %s: user name */
		$message = sprintf( __( 'Password changed for user: %s' ), $user->user_login ) . "\r\n";
		// The blogname option is escaped with esc_html on the way into the database in sanitize_option
		// we want to reverse this for the plain text arena of emails.
		$blogname = wp_specialchars_decode(get_option('blogname'), ENT_QUOTES);

		$wp_password_change_notification_email = array(
			'to'      => get_option( 'admin_email' ),
			/* translators: Password change notification email subject. %s: Site title */
			'subject' => __( '[%s] Password Changed' ),
			'message' => $message,
			'headers' => '',
		);

		/**
		 * Filters the contents of the password change notification email sent to the site admin.
		 *
		 * @since 4.9.0
		 *
		 * @param array   $wp_password_change_notification_email {
		 *     Used to build wp_mail().
		 *
		 *     @type string $to      The intended recipient - site admin email address.
		 *     @type string $subject The subject of the email.
		 *     @type string $message The body of the email.
		 *     @type string $headers The headers of the email.
		 * }
		 * @param WP_User $user     User object for user whose password was changed.
		 * @param string  $blogname The site title.
		 */
		$wp_password_change_notification_email = apply_filters( 'wp_password_change_notification_email', $wp_password_change_notification_email, $user, $blogname );

		wp_mail(
			$wp_password_change_notification_email['to'],
			wp_specialchars_decode( sprintf( $wp_password_change_notification_email['subject'], $blogname ) ),
			$wp_password_change_notification_email['message'],
			$wp_password_change_notification_email['headers']
		);
	}
}