title: Custom taxonomy with hierarchical url link structure
body: <p>I created a custom taxonomy called instrument_categories. It works fine but I want the link structure to be like this:</p>
  
  <pre><code>www.example.com/instruments/term/subterm
  </code></pre>
  
  <p>Instead, I get this:</p>
  
  <pre><code>www.example.com/instruments/term/
  www.example.com/instruments/subterm
  </code></pre>
  
  <p>I've read a dozen posts about this, and I can't find anything wrong with my code:</p>
  
  <pre><code> add_action( 'init', 'create_instrument_taxonomies', 0 );
  
   function create_instrument_taxonomies()
   {
     // Add new taxonomy, make it hierarchical (like categories)
     $labels = array(
       'name' =&gt; _x( 'Instrument Categories', 'taxonomy general name' ),
       'singular_name' =&gt; _x( 'Instrument Category', 'taxonomy singular name' ),
       'search_items' =&gt;  __( 'Search Instrument Categories' ),
       'popular_items' =&gt; __( 'Popular Instrument Categories' ),
       'all_items' =&gt; __( 'All Instrument Categories' ),
       'parent_item' =&gt; __( 'Parent Instrument Category' ),
       'parent_item_colon' =&gt; __( 'Parent Instrument Category:' ),
       'edit_item' =&gt; __( 'Edit Instrument Category' ),
       'update_item' =&gt; __( 'Update Instrument Category' ),
       'add_new_item' =&gt; __( 'Add New Instrument Category' ),
       'new_item_name' =&gt; __( 'New Instrument Category Name' ),
     );
         register_taxonomy('instrument_categories',array('sdp_instrument'), array(
           'hierarchical' =&gt; true,
           'labels' =&gt; $labels,
           'show_ui' =&gt; true,
           'query_var' =&gt; true,
           'rewrite' =&gt; array( 'slug' =&gt; 'instruments', 'hierarchal' =&gt; true, 'with_front' =&gt; true ),
         ));
   }
  </code></pre>
  
  <p>Am I missing something? I've made sure to refresh the permalinks. Why won't this work?</p>