1 <?php 2     $title="hello";   //正确 3     $title123="hello";  //正确 4     $123title="hello";  //错误 5     $_title="hello";     //正确 6     $@#title="hello";   //错误 7     $url="hello";   //我们得到一个变量url 8     echo $url;      //结果：hello 9     unset($url);   //删除一个变量url10     echo $url;     //结果为空11 ?>