def submit_form_id(self, id_):
    """
    Submit the form with given id (used to disambiguate between multiple
    forms).
    """
    form = ElementSelector(
        world.browser,
        str('id("{id}")'.format(id=id_)),
    )
    assert form, "Cannot find a form with ID '{}' on the page.".format(id_)
    form.submit()