Checkbox invalid mock data
label:
$tpl: elements/form-element/label
$ref: elements/form-element/label
for: form-element-input8
type: checkbox
label_display: after
children:
$tpl: elements/form-element/option
$ref: elements/form-element/option#checkbox-invalid
id: form-element-input8
errors: <p>This is an error message.</p>