php使用框架呈现的奇怪问题

php代码如下：<?
    echo '
        <html>
        <head>
        <meta http-equiv="Content-Type" content="text/html; charset=gb2312">
        <title>内容管理系统</title>
        </head>
        
        <frameset rows="118,*" cols="*" frameborder="NO" border="0" framespacing="0">
          <frame src="header.php" name="topFrame" scrolling="NO" noresize >
          <frameset rows="*" cols="160,*" framespacing="4" frameborder="YES" border="4">
            <frame src="left.php" name="leftFrame" id="leftFrame" scrolling="NO">
            <frame id="mainFrame" src="welcom.php" name="mainFrame">
          </frameset>
        </frameset>
        <noframes><body>
        </body></noframes>
        </html>
        ';
?>