echo Html::dropDownList('country', null, [ 'US' => 'United States', 'UK' => 'United Kingdom', 'CA' => 'Canada', ]);
echo Html::dropDownList('gender', 'Unknown', [ 'M' => 'Male', 'F' => 'Female', ], ['prompt' => 'Select Gender']);
echo Html::dropDownList('colors[]', null, [ 'Red' => 'Red', 'Green' => 'Green', 'Blue' => 'Blue', ], ['multiple' => 'multiple']);In this example, a dropdown list is generated with multiple select options. The `colors[]` parameter name is used to store the selected options in an array. The `multiple` option is used to allow the user to select more than one option from the list. Package Library: `yii2/helpers`