WordPress at a glance
filter is not described

the_category_rss filter-hook . WP 1.2.0

Filters all of the post categories for display in a feed.

Usage

add_filter( 'the_category_rss', 'filter_function_name_2229', 10, 2 );
function filter_function_name_2229( $the_list, $type ){
	// filter...

	return $the_list;
}
$the_list(string)
All of the RSS post categories.
$type(string)
Type of feed. Possible values include 'rss2', 'atom'.
Default: 'rss2'

Where the hook is called

get_the_category_rss()
the_category_rss
wp-includes/feed.php 414
return apply_filters( 'the_category_rss', $the_list, $type );

Where the hook is used (in WP core)

Does not used.