How add a class to a label element with Symfony forms?

Question

I have a FormBuilderwith Symfony3 and I need you to add a class to the discount label. How can you observe the third parameter of the add method is an array and a key is attr which has another array with the attributes of the input element, but not the label.

How can I add class to the label?

 $builder
->add('note', TextareaType::class, array(
    'label' => "Notes",
    'required' => false
))
->add('discount', NumberType::class, array(
    'required' => false,
    'attr' => array(
        'class' => "hidden"
    )
))

Answer 1

You can see the label_attr parameter in symfony docs

'label'=>"Notes,array('label_attr' => array('class' => 'class_name'))"