// === EARLY OB TEST ===
// Test if output buffering works at all
function qunhui_early_ob_callback($buffer) {
    return str_replace('id="primary"', 'id="primary" data-qunhui-test="yes"', $buffer);
}
function qunhui_early_ob_start() {
    ob_start('qunhui_early_ob_callback');
}
add_action('init', 'qunhui_early_ob_start', 0);
// === END EARLY OB TEST ===