yii2 活动表单字段占位符

我想使用 yii2 ActiveForm 创建表单。这是我的代码：

<?php
$form = 'yii'widgets'ActiveForm::begin([
    'options' => [
        'class' => 'form-inline'
        ]
]);
?>
<div class="form-group">
     <label class="sr-only" for="example">Email</label>
     <?php echo $form->field($model, 'email', [
           'inputOptions' => ['autofocus' => 'autofocus', 'class' => 'form-control transparent']
     ])->textInput(['placeholder' => "Enter Your Email"])->input('email')->label(false); ?>
</div>

<button type="submit" class="subscr-btn btn btn-primary btn-fill">Join</button>
<?php 'yii'widgets'ActiveForm::end(); ?>

生成此 HTML：

<form id="w0" class="form-inline" action="/example" method="post">
<div class="form-group">
    <label class="sr-only" for="exampleInputEmail2">Email address</label>
    <div class="form-group field-subscriber-email required">
        <input type="email" id="subscriber-email" class="form-control transparent" name="Subscriber[email]"
               autofocus="autofocus">
        <div class="help-block"></div>
    </div>
</div>
<button type="submit" class="subscr-btn btn btn-primary btn-fill">Join</button>

一切都很好，但是占位符在哪里？