title: WordPress: How to return value when use add_filter?
body: <p>I've read WordPress codex many times but still don't understand how to return the value if more than one arguments involved. For example:</p>
  
  <pre><code>function bbp_get_topic_title( $topic_id = 0 ) {
      $topic_id = bbp_get_topic_id( $topic_id );
      $title    = get_the_title( $topic_id );
  
      return apply_filters( 'bbp_get_topic_title', $title, $topic_id );
  }
  </code></pre>
  
  <p>In the above filter, there are 2 arguments. When I <code>add_filter</code>, should I return 2 value, or just return the one I need? Is the following example correct if need the title?</p>
  
  <pre><code>add_filter( 'bbp_get_topic_title', 'my_topic_title', 10, 2 );
  
  function my_topic_title( $title, $topic_id ){
    $title = 'my_example_title';
    return $title;
  }
  </code></pre>