Hierarchical taxonomy in permalink structure

Add the value you want before the “meaningful” url variables (city, area, etc) to the slug like this:

"uk/([^/]*)/([^/]*)/?$" => 'index.php?city=$matches[1]&area=$matches[2]&something=$matches[3]',

This way it will only “capture” those URL variables (city, area) if “uk” is at the beginning.

A more complete example might look like this

//Set up the additional values in the "rewrite rules" array
function my_rewrites($rules){

        $new_rules = array(

            //uk/London/Chelsea/
            "uk/([^/]*)/([^/]*)/?$" => 'index.php?city=$matches[1]&area=$matches[2]',

        );

        $new_rules = array_merge($new_rules, $rules);

        return $new_rules;
}
add_filter('rewrite_rules_array', 'my_rewrites');


/**
 * Add Rewrite Tags 
 */
function my_rewrite_tags(){

    //EG "London"
    add_rewrite_tag('%city%','([^/]*)');

    //EG "Chelsea"
    add_rewrite_tag('%area%','([^/]*)');

}
add_action('init', 'my_rewrite_tags');

/**
 * Use the information provided in the URL like this:
 */
function my_custom_function_which_does_stuff(){
    global $wp_query;

    if ( isset( $wp_query->query_vars['city'] ) ){

        //EG London
        $city = $wp_query->query_vars['city'];

        //EG Chelsea
        $area = $wp_query->query_vars['area'];

    }

}
add_action( 'init', 'my_custom_function_which_does_stuff' );

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