Why does the use of the Frameset DTD cause a validation failure?
The project I work on takes random HTML files, converts them to XHTML as best as it can, and wraps them with some XML metdata. The DOCTYPE is stripped out as the resulting XML file is not an XHTML document. However when retrieving the wrapped XHTML from the XML file the DOCTYPE should be reinserted.
Because these are random HTML files they could contain any content, but I would prefer to not have to store or determine the original DTD. I figured that I should the Frameset DTD as it was just a superset of the Transitional DTD and would be valid for all content. However when using the W3C XHTML Validator with the same document, using the Transitional DTD passes but using the Frameset DTD fails.
I've stripped down the document to the minimum with which I can reproduce the problem. Here is the Frameset version:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:html="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Make The Move</title>
</head>
<body style="background: none;">
<h3 id="why">Why should I move to Linux?</h3>
</body>
</html>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:html="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="te开发者_JS百科xt/html; charset=UTF-8" />
<title>Make The Move</title>
</head>
<body style="background: none;">
<h3 id="why">Why should I move to Linux?</h3>
</body>
</html>
Frameset DTD is not a 'superset' of transitional. It is a special DTD only used for laying out frames, not content (except inside <noframes> tag). It allows only <head> and <frameset> as the children of <html> tag.
Here is the specification.
Unless you know your page could have frames, stick to transitional or strict DTDs.
As Chetan pointed out, the Frameset DTD should only be used in case you need frames, and even then, I would recomend on using Transitional instead. If you don't rely on frames, Strict is the way to go.
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