About This HTML Issue
The <noframes> element is obsolete, so remove it and move any content worth keeping into the page's <body> as regular markup.
<noframes> held fallback content for browsers that couldn't display a <frameset>. Every browser in use today displays frames, and the rendering rules in the HTML standard hide <noframes> with display: none wherever it appears, so visitors never see what's inside it. The parser also reads its contents as raw text, the same way it reads a <style> element, so the validator doesn't check the markup inside it either.
The validator reports <noframes> wherever it sits: inside a <frameset>, after the closing </frameset>, in the <head> or in a regular <body>. In the <head> and after </frameset> it also adds an error saying the element isn't allowed there, and that error goes away with this one.
What to do depends on the page around it. In a frameset document, <noframes> goes away together with the <frameset> and its <frame> elements, which get obsolete messages of their own. The fallback often already holds a frameless version of the page, such as links to the documents the frames loaded, and that content can become the start of the new <body>. When <noframes> is left over in a page that already has a <body>, usually copied from an old template, delete it. Nothing inside it was ever displayed, so the page looks the same without it.
Don't move the fallback into an <iframe> instead. An iframe has to stay empty, and the validator reports any content placed inside it.
Invalid example
A two-frame page with a fallback for browsers without frame support:
<!DOCTYPE html>
<html lang="en">
<head>
<title>Club newsletter</title>
</head>
<frameset cols="25%,75%">
<frame src="issues.html">
<frame src="latest.html">
<noframes>
<body>
<p>This site uses frames. Read the <a href="latest.html">latest issue</a> or browse the <a href="issues.html">past issues</a>.</p>
</body>
</noframes>
</frameset>
</html>
Valid example
The frameset becomes a <body>, the links from the fallback become the page's navigation, and an <iframe> loads the issue the second frame used to show:
<!DOCTYPE html>
<html lang="en">
<head>
<title>Club newsletter</title>
</head>
<body>
<nav>
<a href="latest.html" target="issue">Latest issue</a>
<a href="issues.html" target="issue">Past issues</a>
</nav>
<iframe src="latest.html" name="issue" title="Newsletter issue"></iframe>
</body>
</html>
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