Removed references to itemprop / microdata

[halindrome]

Microdata was removed from HTML development in 2013. The microdata
related attributes were still embedded in the spec. This pull request
removes those. It also changes the examples that use microdata to
examples that use RDFa Lite. RDFa Lite is a W3C Recommendation, so is
more appropriate to use for examples.

[chaals]

I suspect we should revert this and make a more thorough change.

Microdata is actually used pretty widely, and is read e.g. by search engines, so it seems a relevant candidate to make a short extension spec as a Rec.

Meanwhile, I agree that we should also have RDFa examples.

Finally, I think we should incorporate the relevant attributes - both sets should (IMHO) be valid for HTML, so included in the spec but linked to the relevant external specs rather than contained in the text of HTML itself. I'll raise an issue in the next few days, if nobody beats me to it.

[halindrome]

@chaals I don't disagree. And please don't take this as my meaning I an offended that you want to back out my change. I assumed this was an editorial error and tried to fix it in a way that was consistent with my understanding of W3C process and the intent of the evolution of HTML5. With that in mind, a couple of things:

1. I know there is a microdata Note. I am not sure what the status of that Note and its ownership is. Extension specs need to be Rec Track. If there is energy for a Rec Track spec on microdata, great. I know it is widely used . If not, then I would not support introducing normative dependencies on it.
2. There are already some existing extension specs (e.g., RDFa in HTML, HTML5 Image Description). My understanding is that, once they are W3C Recommendations, they are a normative part of HTMLn. Is there a policy for how Recommendations will be referenced by the core HTMLn spec?
3. The HTMLn document the W3C produces is not a "living standard" as I understand it. It is agile but not fluid. Presumably the W3C will not be including material in an HTMLn until it is either part of an extension Recommendation or intended to be balloted upon for inclusion in the HTMLn spec itself. Is that correct?

[chaals]

1. Yeah, in order to produce a normative dependency we should have a Rec. Given that the attributes and so on are part of HTML5, it should be simple to pull that out.
2. Thus far we're not quite sure. I'll raise an issue, but the way that seems simplest to me is that the relevant hooks like attributes should go into the main document, but that they should direct to the specific extension to explain the meaning, etc.
3. That matches my understanding.

[paulbrucecotton]

There is a lot of history on why/how Microdata material was removed from HTML5 and why some of the Microdata material was published as a WG Note. I hope some of the information below is useful.

First the HTML WG agreed to publish the Microdata material in a separate Recommendation track specification in 2010:
https://lists.w3.org/Archives/Public/public-html/2010Jan/att-0218/issue-76-decision.html

Subsequently the HTML WG decided to keep the separate Microdata specification on the Recommendation track in 2013:
https://lists.w3.org/Archives/Public/public-html-admin/2013Jan/0022.html
https://lists.w3.org/Archives/Public/public-html-admin/2013Jan/0182.html

In early 2013 when we tried to take the Microdata specification to Candidate Recommendation, we discovered problems with the specification (ie missing section) and that forced the HTML WG to once again consider its position on the separate Recommendation track specification.

The HTML WG discussed various options for the Microdata attributes and API at a F2F meeting in Spring 2013. The following email summarizes the options:
https://lists.w3.org/Archives/Public/public-html-admin/2013Apr/0064.html

The HTML WG then considered the following Call For Consensus on how to handle the Microdata material:
https://lists.w3.org/Archives/Public/public-html-admin/2013May/0000.html
There were initial objections to this CfC and after a WG meeting in July another CfC was sent:
https://lists.w3.org/Archives/Public/public-html-admin/2013Jul/0019.html

Since there were no objections to this 2nd CfC the HTML WG decided handle the Microdata attributes and API as follows:
https://lists.w3.org/Archives/Public/public-html-admin/2013Jul/0041.html

"The Editors are requested to carry out the directions of the CfC:
    a) to remove all references to Microdata from the HTML 5.0 CR draft,
    b) to remove the Javascript API from the Microdata spec, and
    c) to publish the separate "HTML Microdata" document as an extension spec (iff editorial resources can be found)."

The following bug documents how the Editors implemented item a) from the above list:
https://www.w3.org/Bugs/Public/show_bug.cgi?id=22783

Subsequently the Chairs tried to find an editor for the "HTML Microdata" extension specification. The call for volunteers is here:
https://lists.w3.org/Archives/Public/public-html-admin/2013Aug/0059.html

When no one stepped forward to edit the extensions specification, the HTML WG agreed to publish the remaining "HTML Microdata" material (without the API) as a WG Note. See the HTML WG Decision:
https://lists.w3.org/Archives/Public/public-html-admin/2013Oct/0094.html

Note that since the Web Platform WG's version of HTML5.1 was based directly on a WHATWG version of HTML, I believe it might also be useful to research how the Microdata attributes and API were handled in the WHATWG specification. It is certainly possible that the material identified in this bug was simply not removed from the upstream WHATWG version of HTML in the same way as described in https://www.w3.org/Bugs/Public/show_bug.cgi?id=22783.

/paulc