How to add collapsible help text to a form? I would like to add some collapsible text underneath my comment forms. Preferably, users can click a small icon, which reveals the help text. After reading https://stackoverflow.com/a/8405715/2625920, I already added a paragraph at the desired position:

function MYTHEME_form_comment_form_alter(&amp;$form, &amp;$form_state) {
  $form['markup'] = array(
    '#markup' =&gt; t('&lt;p&gt;Here is some very useful text.&lt;/p&gt;'),
    '#weight' =&gt; -1,
  );
}


(Actually, it surprised me that this works, since #markup is not ticked for forms in the Form API Reference...) Unfortunately, simply adding

'#collapsible' =&gt; TRUE,
'#collapsed' =&gt; TRUE,


to the array does not work (which is expected according to the Form API Reference). Any suggestions?
What about putting it into a fieldset ? 

$form['fieldset'] = array(
 '#title' =&gt; 'title',
 '#type' =&gt; 'fieldset',
 '#collapsible' =&gt; TRUE,
 '#description' =&gt; 'desc',
);

$form['fieldset']['some_text'] = array(
  '#markup' =&gt; '&lt;p&gt;Here is some very useful text.&lt;/p&gt;',
  '#weight' =&gt; -1,
);