How can 'markup' type elements take #attributes?

), your content will fall outside of collapsed fieldsets."
and:
"Properties: #attributes, #prefix (default: ''), #suffix (default: ''), #type. #value, #weight"

If the content doesn't get wrapped, then there's nothing for attributes to apply to, surely?
The following code does nothing with the class, for example:

  $form['image'] = array(
    '#prefix' => '<div>',
    '#value' => '<p>hello</p>',
    '#suffix' => '</div>',
    '#attributes' => array('class' => 'attribute-class'),   
    );