WordPress at a glance
function is not described

welcome_user_msg_filter() WP 3.0.0

Ensure that the welcome message is not empty. Currently unused.

No Hooks.

Return

String.

Usage

welcome_user_msg_filter( $text );
$text(string) (required)

Code of welcome user msg filter: wp-includes/ms-functions.php VER 5.0.3

<?php
function welcome_user_msg_filter( $text ) {
	if ( !$text ) {
		remove_filter( 'site_option_welcome_user_email', 'welcome_user_msg_filter' );

		/* translators: Do not translate USERNAME, PASSWORD, LOGINLINK, SITE_NAME: those are placeholders. */
		$text = __( 'Howdy USERNAME,

Your new account is set up.

You can log in with the following information:
Username: USERNAME
Password: PASSWORD
LOGINLINK

Thanks!

--The Team @ SITE_NAME' );
		update_site_option( 'welcome_user_email', $text );
	}
	return $text;
}