core/Fields/Definitions/templates/code/default.twig
{% extends Form.getLayout() %}
{% block fieldmarkup %}
<textarea id='{{ Form.getInputFieldId() }}' name='{{ Form.getFieldName() }}'
placeholder='{{ Form.getPlaceholder() }}'
{% for attr, value in Field.getArg('attributes', []) %}
{{ attr }}="{{ value|esc_attr }}"
{% endfor %}>{{ Field.getValue() }}</textarea>
{% endblock %}