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Re: [cc-devel] Malformed HTML in CC licences

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  • From: Richard Smith <richard AT ex-parrot.com>
  • To: cc-devel AT lists.ibiblio.org
  • Subject: Re: [cc-devel] Malformed HTML in CC licences
  • Date: Thu, 5 Jan 2012 12:23:00 +0000 (GMT)
Nathan Yergler wrote:

Yikes. Regardless of whether they're well formed as XML, these do need
to be well formed HTML to fulfill the promise that they operate as
linked data documents.

Thanks for your reply. I agree it needs to be well-formed HTML, but this needn't mean HTML 4. Everything I've read that purports to be a standard on linked data documents allows for XHTML dialects too. As the CC licences are generated with 'transitional' XHTML 1.0 <!DOCTYPE> declarations, presumably they are intended to be in that dialect. And if so, well-formed XHTML 1.0 simply means well-formed XML.

We can probably never have totally valid XHTML (as opposed to well-formed XHTML) because the RDFa attributes such as 'about' and 'resource' are not valid XHTML. Nor are the extra namespace declarations needed on the <html> element. But parsers don't need to validate so that shouldn't be a problem.

In the case of the extraneous span close tag,
that looks like a bug in the template
(http://code.creativecommons.org/viewgit/cc.engine.git/tree/cc/engine/templates/licenses/standard_deed.html#n167)
that's going to be present in every core deed generated.

I guessed there must have been a template somewhere, but hadn't managed to locate it.

The </span> is the major problem here as it is the only one current parsers are not reliable at recovering from, and it's unambiguously an error: the line simply needs deleting. Is posting here sufficient to get that fixed? If not, what should I do?

But if we marking the document as XHTML and therefore XML, we really should correct the other well-formedness issues. The three unescaped ampersands are generated on this line:


http://code.creativecommons.org/viewgit/cc.engine.git/tree/cc/engine/templates/macros_templates/deed.html#n143

Each instances of '&' simply need replacing with '&amp;'. This is a legitimate (but not usually necessary) thing to do in HTML 4, but is necessary with XHTML's stricter parsing rules. A discussion on this incompatibility can be found here:

http://www.w3.org/TR/xhtml1/#C_12

but the summary is that it is always a good idea to escape the '&' in this manner.

The two unescaped '<' signs are generated on this line:


http://code.creativecommons.org/viewgit/cc.engine.git/tree/cc/engine/templates/macros_templates/deed.html#n163

In this context, HTML 4 prohibits '<' being escaped as &lt; while XHTML mandates it. For maximum compatibility we probably want our document to work when parsed as HTML or as XHTML, and there are two types of trick that can be used to fix this. The most flexible is to use a <![CDATA]> section that will appear to be commented out to a HTML 4 parser. This is described here:

http://javascript.about.com/library/blxhtml.htm

We would simply change

document.write( ... );

to

/* <![CDATA[ */
document.write( ... );
/* ]]> */

These changes are all harmless to a HTML 4 parser, but make the difference between the document being well-formed XHTML or not.

Richard


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