Do older files works on new browsers?

Answer 1

If you mean HTML documents wriiten in previous HTML standards, then yes, browsers are mostly written with backward compatibility in mind, and be forgiving about syntax errors.

But that doesn't mean it will be supported forever, sooner or later deprecated tags will be removed from list of supported tags.

Answer 2

Yeah got the answer...
Thanks Lyk Videx, Martin Taylor , Ipang for the explanation👍