title: How to hook page_attributes_meta_box to change displaying "Parent" option?
body: <p>At WP Admin panel there are "Attributes" metabox with "Parent" dropdown list.
  I need to change sort parameters and show only parent posts.
  I may do it if I change native WP file <strong>meta-boxes.php</strong> line <strong>621</strong>. Following code:</p>
  
  <pre><code>$dropdown_args = array(
      'post_type'        =&gt; $post-&gt;post_type,
      'exclude_tree'     =&gt; $post-&gt;ID,
      'selected'         =&gt; $post-&gt;post_parent,
      'name'             =&gt; 'parent_id',
      'show_option_none' =&gt; __('(no parent)'),
      //Remove existing sort
      //'sort_column'      =&gt; 'menu_order, post_title',
      'echo'             =&gt; 0,
      //Add my options
      'parent'           =&gt; 0,
      'sort_order'       =&gt; 'DESC',
      'sort_column'      =&gt; 'post_date',
  );
  </code></pre>
  
  <p>Using this all work perfect. But i need to hook it. I have created actiont to do it, but it does not works:</p>
  
  <pre><code>add_action('page_attributes_meta_box', 'custome_page_attributes_meta_box');
  function custome_page_attributes_meta_box($post) {
      $post_type_object = get_post_type_object($post-&gt;post_type);
      if ( $post_type_object-&gt;hierarchical ) {
          $dropdown_args = array(
              'post_type'        =&gt; $post-&gt;post_type,
              'exclude_tree'     =&gt; $post-&gt;ID,
              'selected'         =&gt; $post-&gt;post_parent,
              'name'             =&gt; 'parent_id',
              'show_option_none' =&gt; '(no parent)',
              'echo'             =&gt; 0,
              'sort_order'       =&gt; 'DESC',
              'sort_column'      =&gt; 'post_date',
              'parent'           =&gt; 0
          );
  
          $dropdown_args = apply_filters( 'page_attributes_dropdown_pages_args', $dropdown_args, $post );
          $pages = wp_dropdown_pages( $dropdown_args );
          if ( ! empty($pages) ) {
          ?&gt;
              &lt;p&gt;&lt;strong&gt;&lt;?php _e('Parent') ?&gt;&lt;/strong&gt;&lt;/p&gt;
              &lt;label class="screen-reader-text" for="parent_id"&gt;&lt;?php _e('Parent') ?&gt;&lt;/label&gt;
              &lt;?php echo $pages; ?&gt;
          &lt;?php
          } // end empty pages check
      } // end hierarchical check.
  }
  </code></pre>
  
  <p>What I am doing wrong?</p>