Microdata

 Microdata  is a method of embedding metadata in web pages. It is currently a W3C Working Draft.

More complex than microformats

 * Microdata is a more complex way of adding metadata to HTML than microformats. There is no browser support for it. See http://www.kevinmarks.com/microformatschema.html for a markup comparison

Too complex to do by hand
https://twitter.com/apyth/status/1028343521009459200 (can’t tell if this is specifically criticism about microdata or rel= )
 * "Caveat: microdata is definitely too complex to do by hand though" @apyth August 11, 2018