pdnew/themes/default/templates/form/button/button-submit.html

<button
    {% if not content.id is none %}
        id="{{ content.id }}"
    {% endif %}
    name="submit"
    {% if content.prefix %}
        value="{{ content.prefix}}.{{ content.name }}"
    {% else %}
        value="{{ content.name }}"
    {% endif %}
>{{ content.label }}</button>