// Simple mailto link with email address echo Html::mailto('test@example.com'); // Mailto link with email address and subject echo Html::mailto('test@example.com', 'Email Subject'); // Mailto link with email address, subject and body echo Html::mailto('test@example.com', 'Email Subject', 'Email Body', ['class' => 'btn btn-primary']);In these examples, the `Html` class is used to generate mailto links with different parameters such as email address, subject, body, and CSS classes. The fourth parameter is used to set additional attributes for the generated anchor tag. This feature is part of the Yii web application framework, specifically the `yii\helpers\Html` class, which is included in the core framework package.