add html to fieldset I try to customize fieldset ABC that are inside drupal commerce checkout page.
Markup looks like this

&lt;fieldset&gt;
 &lt;legend&gt;ABC&lt;/legend&gt;
 &lt;div class="fieldset-wrapper"&gt;
  &lt;div class="form-item"&gt;&lt;/div&gt;
  &lt;div class="form-item"&gt;&lt;/div&gt;
 &lt;/div&gt;
&lt;/fieldset&gt;


I would like to put some additional code directly inside fieldset and then also some other html directly inside form-item elements. 
Question> What should I do to achieve that? I found this page https://api.drupal.org/api/drupal/includes!form.inc/function/theme_fieldset/7 would it be of any help? Thank you.

images
Try to change it using hook_form_FORM_ID_alter().

// Replace FORM_ID with commerce checkout form id
function hook_form_FORM_ID_alter($form, &amp;$form_state, $form_id) {
  $form['fieldset_item']['mymarkup'] = array(
    '#type' =&gt; 'item',
    '#markup' =&gt; 'My Markup Here.',
  );
}