Clarify steps when embed tag has unhandled MIME type #3876
Description
When an embed tag has an unhandled MIME type, there are no explicit steps about what to do. By the current setup steps, we'd end up at:
Otherwise, the content has no type and there can be no appropriate plugin for it.
But this doesn't explicitly say what to do with the content. In the case of object, we know to follow the fallback path (https://html.spec.whatwg.org/multipage/iframe-embed-object.html#the-object-element).
Testing across browsers using:
<html>
<head>
</head>
<body>
<embed src="https://example.com" type="application/whatever" />
</body>
</html>- Chrome: Shows "Missing Plugin" UI
- Safari: Shows "Missing Plugin" UI
- Firefox: Currently parses src as a document type, will be dropping processing with no "Missing Plugin" UI once relevant bug lands
- Edge: Parses src as document type and shows in embedded frame