$multiselect = [
	'type' => 'multiselect',
	'options' => [ '1' => '1', '2' => '2' ],
	'required' => true,
	'default' => [ '1', '2' ]
];
$normal = [ 'label' => 'plain' ];
$dropdown = [ 'label' => 'dropdown', 'dropdown' => true, ];
$hidden = [ 'hide-if' => [ '===', 'hider', 'hide' ] ];
$form = HTMLForm::factory( 'ooui', [
	'hider' => [
		'type' => 'select',
		'options' => [ 'hide' => 'hide', 'show' => 'show' ],
		'default' => 'hide',
	],
	'plain' => $multiselect + $normal,
	'dropdown' => $multiselect + $dropdown,
	'plain-hidden' => $multiselect + $normal + $hidden,
	'dropdown-hidden' => $multiselect + $dropdown + $hidden,
], RequestContext::getMain() );
$form->setSubmitCallback( function ( $vals ) {
	var_dump( $vals );
	return true;
} );
$form->show();