Is it possible to use tags (letters/words) that you want in HTML?

Question

HTML

In general, 5 years ago I tried to wrap the text in a non-existent tag and set a style for it, and it worked.
Now I remembered, I decided to try to experiment, it turns out that you can enter any letter, or even a word, thereby creating your own tag. For example, the usual one can be replaced with and it will work.
Who looks at this, whether such a method has any contraindications or disadvantages, if there are any, I would like to hear.
By the fact that it seems to be a cool thing, but I have not seen this anywhere.
jsfiddle.net/vjq87bd2/1

Answer 1

Can.
www.smashingmagazine.com/2014/03/introduction-to-c...
www.html5rocks.com/en/tutorials/webcomponents/cust...

Answer 2

Not