Submit the form with the given action URL (i.e. the form that submits to
    ``/post/my/data``).

def submit_form_action(self, url):
    """
    Submit the form with the given action URL (i.e. the form that submits to
    ``/post/my/data``).
    """
    form = ElementSelector(
        world.browser,
        str('//form[@action="%s"]' % url),
    )
    assert form, \
        "Cannot find a form with action '{}' on the page.".format(url)
    form.submit()