Provides a render element that wraps child elements in a container.
Surrounds child elements with a <div> and adds attributes such as classes or an HTML ID.
Usage example:
$form['needs_accommodation'] = array(
'#type' => 'checkbox',
'#title' => $this->t('Need Special Accommodations?'),
);
$form['accommodation'] = array(
'#type' => 'container',
'#attributes' => array(
'class' => 'accommodation',
),
'#states' => array(
'invisible' => array(