add another filter add_valid_class?

[BoPeng]

bootstrap allows the use of is-valid and is-invalid for fields of validated forms (bounded). Whereas is-invalid class can be easily added as

 {% render_field form.field1|add_error_class:'is-invalid' %}

It is not easy to do so with is-valid because blindly adding the class will mark fields as valid for unbounded forms.

Is it possible to add another filter called add_valid_class as follows?

@register.filter("add_valid_class")
@silence_without_field
def add_valid_class(field, css_class):
    if field.form.is_bound and not (hasattr(field, "errors") and field.errors):
        return add_class(field, css_class)
    return 

I suppose it also makes sense to add WIDGET_VALID_CLASS so that I can do

{% with WIDGET_ERROR_CLASS='is-invalid' WIDGET_VALID_CLASS="is-valid" %}
    {% render_field form.field1 %}
    {% render_field form.field2 %}
    {% render_field form.field3 %}
{% endwith %}