The ID of an element referenced by a `label`s ``for`` attribute. The label
    must be visible.

    :param browser: ``world.browser``
    :param label: label text to return the referenced element for

    Returns: ``for`` attribute value

def element_id_by_label(browser, label):
    """
    The ID of an element referenced by a `label`s ``for`` attribute. The label
    must be visible.

    :param browser: ``world.browser``
    :param label: label text to return the referenced element for

    Returns: ``for`` attribute value
    """
    label = ElementSelector(browser,
                            str('//label[contains(., %s)]' %
                                string_literal(label)))
    if not label:
        return False
    return label.get_attribute('for')