Source Reference:

• Component: bbPress :: bbp-admin

  File: /bbp-admin/bbp-metaboxes.php :: Trac Source Line: 428

  		'selected'    => $reply_topic_id,
  		'select_id'   => 'parent_id',
  		'orderby'     => 'post_date',
  		'numberposts' => '250',
  		'show_none'   => is_super_admin() ? __( '(No Topic)', 'bbpress' ) : '',
  	);
  
  	// Allow the dropdown to be filtered, to extend or limit the available
  	// topics to choose as the reply parent.
  	$args = apply_filters( 'bbp_reply_parent_dropdown', $args ); ?>
  
  	<p><strong><?php _e( 'Topic', 'bbpress' ); ?></strong></p>
  
  	<p>
  		<label class="screen-reader-text" for="parent_id"><?php _e( 'Topic', 'bbpress' ); ?></label>
  
  		<?php bbp_dropdown( $args ); ?>
  
  	</p>