WordPress at a glance
filter is not described

wp_list_categories filter-hook . WP 2.1.0

Filters the HTML output of a taxonomy list.

Usage

add_filter( 'wp_list_categories', 'filter_function_name_3725', 10, 2 );
function filter_function_name_3725( $output, $args ){
	// filter...

	return $output;
}
$output(string)
HTML output.
$args(array)
An array of taxonomy-listing arguments.

Where the hook is called

wp_list_categories()
wp-includes/category-template.php 635
$html = apply_filters( 'wp_list_categories', $output, $args );

Where the hook is used (in WP core)

Does not used.