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Comment by onli | Hacker News Reader

This is the RDF needed for trackback support (and like I said, rel=trackback exists as well):

    <!--
        <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
                 xmlns:trackback="http://madskills.com/public/xml/rss/module/trackback/"
                 xmlns:dc="http://purl.org/dc/elements/1.1/">
        <rdf:Description
                 rdf:about="https://www.onli-blogging.de/feeds/ei_1522.rdf"
                 trackback:ping="https://www.onli-blogging.de/comment.php?type=trackback&amp;entry_id=1522"
                 dc:title="Medieval II: Total War"
                 dc:identifier="https://www.onli-blogging.de/1522/Medieval-II-Total-War.html" />
        </rdf:RDF>
    -->

How is that complicated? Where is the link to or the problem with semantics?

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It is wholly pointless.

It is virtually never parsed as RDF. RDF-in-HTML-comments is a horrible antipattern that has no use in the RDF community outside of the weird legacy use case of Trackback.

It is hidden metadata (which can and does break) and violates the DRY principle.

It is as much hidden metadata as is any other of such attempts, like schema.org and what else exists. It is a not so beautiful repetition of stuff that is already in the html, true, but it stems from another way of thinking about metadata. Maybe the RDF community does not like it anymore, but it was a thing.

Note that I'm not fan of this, rel=trackback is what should be used. But it is not complicated to add those tags into a page, which was my point.

The DRY principle in its original form does not apply here: The information in those tags will change when the information in the database changes. They are not hardcoded.

Schema.org RDFa isn't hidden. JSON-LD in a script tag is but that's equivalently goofy.

"stems from another way of thinking about metadata"? Nope. It was a clumsy hack because they actually just wanted to put the <rdf:RDF> tags in the HTML but people would complain about HTML validation so they put it in a comment tag.

At least back then I found it mega complicated, I would have needed to screen the content of the page and find the comments most probably with a RegEx I guess? Then I would need to feed the comment strings I get into a XML parser which would understand namespaces. Then I would go through the DOM of every of those comments to get out the data.

Apart from that I do not think you should compare pingback/webmention with trackback. The ones are to inform about some mention/comment, the other is transporting the content of it. If you want to compare than I would compare microformats/open-graph with trackback.

You probably would not use an XML parser. All the information needed to send a trackback is the ping-location, that is one ugly regexpression, but only one. I also am no fan of that, rel=trackback is nicer. But the (pragmatic approach to) parsing is simpler than you describe.

I'm actually not okay about the distinction. Trackbacks inform and transport the content, and webmentions inform and are coupled with an unspecified convention to get the content. They end up having the same purpose.

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