As you probably know, the HTML <meta> tag is used to specify page metadata while the rel attribute, most notably on <link> tag, is used to link other documents to the page while specifying the exact type of the link. Both have a bunch of standard types, but nothing stops you from just making shit up, which is exactly what projects like Open Graph did. However, recently I’ve been noticing some non-standard ones that aren’t part of a well-known collection like that.
Here’s a couple I’ve just spotted on the website of aria2:
<meta name="HandheldFriendly" content="True">
<meta name="MobileOptimized" content="320">
I’m curious if I’m not alone in this and if anyone has more examples. Send them in this thread if you do.