zxdg_output_manager protocol Lack of isprimaryoutput tag

qt have the concept of primary screen,shouldn't the primary concept be expanded in zxdg_output_manager protocol?

bool QXcbScreen::isPrimaryInXScreen()
{
    auto primary = Q_XCB_REPLY(xcb_randr_get_output_primary, connection()->xcb_connection(), root());
    if (!primary)
        qWarning("failed to get the primary output of the screen");

    const bool isPrimary = primary ? (m_monitor ? m_outputs.contains(primary->output) : m_output == primary->output) : false;

    return isPrimary;
}

the primary screen is designed in some systems to be able to set any screen，primary screen changed,client display will be adjusted