Can I have attributes on closing tags?

Answer 1

Sorry, but it doesn't work and doesn't validate.

If you try other attributes in closing tags, then the browser skips the attribute. I tried it in several ways, tested it with ids and classes, and the css and the javascript didn't recognized them in the ending tag. Your best bet is the commenting.

EDITED

Or you could make your own html tags.

You must use hyphenation, and you should avoid

document.createElement('foo-bar');