Is it possible to specify the name of a class in html tags, which is not defined?

Question

css

Is it possible to specify the name of a class in html tags, which is not defined anywhere? For example, for js purposes. How normal and valid is this?

Answer 1

For js purposes, this is how it is done.

Answer 2

of course it's ok. do not hang IDs :)

Answer 3

Some do this, incl. Me too, albeit rarely. In the designation, for example, that in the next class, a carousel is placed, and in case of edits, immediately finish it. Of course, you can also comment, but there will be too many of them. If the landing page, html can be compressed, comments are useless there. Well, as the person above pointed out, for js, at least it’s more customary for him to use an identifier. It's a matter of taste and whichever suits you best.