可能是这样的：

function my_class_names($classes) {
    $useragent = $_SERVER[\'HTTP_USER_AGENT\'];
    if(strchr($useragent,\'Safari\')) $classes[] = \'Safari\';
    // etc..
    return $classes;
}
add_filter(\'body_class\',\'my_class_names\');

function my_class_names($classes) {
    global $is_lynx, $is_gecko, $is_IE, $is_opera, $is_NS4, $is_safari, $is_chrome, $is_iphone;
    if($is_lynx) $classes[] = \'lynx\';
    elseif($is_gecko) $classes[] = \'gecko\';
    elseif($is_winIE) $classes[] = \'winIE\';
    elseif($is_macIE) $classes[] = \'macIE\';
    elseif($is_opera) $classes[] = \'opera\';
    elseif($is_NS4) $classes[] = \'NS4\';
    elseif($is_safari) $classes[] = \'safari\';
    elseif($is_chrome) $classes[] = \'chrome\';
    elseif($is_iphone) $classes[] = \'iphone\';
    else $classes[] = \'other\';
    return $classes;
}
add_filter(\'body_class\',\'my_class_names\');