$gr_preview_theme = $_GET[\'preview_theme\'];
$gr_preview_css = $_GET[\'preview_css\'];

if (! $gr_preview_css ) 
    $gr_preview_css = $gr_preview_theme;

if($gr_preview_theme && file_exists(get_theme_root() . "/$gr_preview_theme")) {
    add_filter(\'template\',\'use_preview_theme\');
}

if($gr_preview_css && file_exists(get_theme_root() . "/$gr_preview_css")) {
    add_filter(\'stylesheet\',\'use_preview_css\');
}


function use_preview_theme($themename) {
    global $gr_preview_theme;

    return $gr_preview_theme;
}

function use_preview_css($cssname) {
    global $gr_preview_css;

    return $gr_preview_css;
}

pludgin的代码太小。我想把代码放到主题函数中。php文件。我可以这样做吗？

add_filter(\'template\',\'use_preview_theme\');

上面这一行是什么意思？它有什么用？非常感谢。