CKeditor里面写内容如何获取

CKeditor里面写内容怎么获取
这个是调用编辑器的代码 error_reporting(0);
include './ckeditor/ckeditor.php'; //include ckeditor.php
$ckeditor = new CKEditor;

include './ckfinder/ckfinder.php';
$ckeditor->editor('content');
CKFinder::SetupCKEditor($ckeditor, true, true);

?>

我百度用这样的方法：$editor = CKEDITOR.replace("content");
$content=$editor.getData();

但是输出这样的错误Notice: Use of undefined constant CKEDITOR - assumed 'CKEDITOR' in D:\xampp\htdocs\belong\add.php on line 5

Fatal error: Call to undefined function replace() in D:\xampp\htdocs\belong\add.php on line 5 求指导，，，纯属PHP菜鸟

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一直用js 版本的~
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这个可以一句代码获取：
http://www.162100.com/162100editor/
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我是用JS版的
提交时直接获取textarea的ID
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js:
取值：

var text=CKEDITOR.instances.content.getData();

赋值：

CKEDITOR.instances.text1.setData('你好');