Is it OK to use unknown HTML tags?

Question

Correct me if I\'m mistaken, but AFAIK, unknown HTML tags in markup (i.e. tags not defined in the HTML spec, like say, ) will eventually be treate

Answer 1

W3C says:

HTML5 supports unknown tags as inline elements, but it recommends CSS styling for it.

Here is the source: https://www.w3schools.com/html/html5_browsers.asp