New answers tagged markup
Max, Google does support structured data for Organization markups, but they don't support rich snippets for the type. If you change schema.org/Organization to schema.org/LocalBusiness in your markup, you'll see the testing tool results change and the rich snippets displaying. So the error message you're seeing is in regards to rich snippets, not the ...
Although their documentation doesn't say so, using the rel attribute is supported by Google, so both should work. The 'in-URL' ?rel= syntax exists for blog users, who may not have access to edit the page's HTML tags, but the HTML5 separate attribute version is more 'correct' so I'd recommend: <a href="[profile_url]" rel="author">Author</a>
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