How to nest elements in a render array
If an element is given #markup, the render process stops searching for nested elements. To accomplish what you need, just create a second child element with no #prefix or #suffix.

function make_array() {
  $items = port_view_get_block();
  $array = array(
    'container' =&gt; array(
      '#prefix' =&gt; '&lt;div id="container"&gt;',
      '#suffix' =&gt; '&lt;/div&gt;',
      'markup' =&gt; array(
        '#markup' =&gt; 'This is inside the container div',
      ),
      'slider' =&gt; array(
        '#prefix' =&gt; '&lt;div id="slider"&gt;',
        '#suffix' =&gt; '&lt;/div&gt;',
        '#markup' =&gt; 'This is inside the slider div',
      ),
    ),
  );
  return $array;
}