array(
  0 => array(
    node => array(),
  ),
  1 => array(
    node => array(),
  ),
  2 => array(
    node => array(),
  ),
  '#prefix' => '<div id="formatter">';
  '#suffix' => '</div>';
);

function mytemplate_preprocess_field(&$variables) {
  $field_name = $variables['element']['#field_name'];
  if ($field_name == 'field_name') {
    $variables['element']['#prefix'] = '<div class="template-container">';
    $variables['element']['#suffix'] = '</div>';
  }
}

<div id="formatter">
...
</div>