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filter is not described

pre_user_nickname filter-hook . WP 2.0.3

Filters a user's nickname before the user is created or updated.

Usage

add_filter( 'pre_user_nickname', 'filter_function_name_3514' );
function filter_function_name_3514( $nickname ){
	// filter...

	return $nickname;
}
$nickname(string)
The user's nickname.

Where the hook is called

wp_insert_user()
wp-includes/user.php 1579
$meta['nickname'] = apply_filters( 'pre_user_nickname', $nickname );

Where the hook is used (in WP core)

wp-includes/default-filters.php 17
add_filter( $filter, 'sanitize_text_field' );
wp-includes/default-filters.php 18
add_filter( $filter, 'wp_filter_kses' );
wp-includes/default-filters.php 19
add_filter( $filter, '_wp_specialchars', 30 );