WordPress at a glance
filter is not described

mod_rewrite_rules filter-hook . WP 1.5.0

Filters the list of rewrite rules formatted for output to an .htaccess file.

Usage

add_filter( 'mod_rewrite_rules', 'filter_function_name_1905' );
function filter_function_name_1905( $rules ){
	// filter...

	return $rules;
}
$rules(string)
mod_rewrite Rewrite rules formatted for .htaccess.

Where the hook is called

WP_Rewrite::mod_rewrite_rules()
wp-includes/class-wp-rewrite.php 1512
$rules = apply_filters( 'mod_rewrite_rules', $rules );

Where the hook is used (in WP core)

Does not used.