Is there any difference between
and
It is all about the true validity of HTML markup. It's for what W3C (WWW Consortium) work for. Many things might work in HTML but they have to be validated in order to be more carefully recognized by the web browser. You can even omit the and
tags at the start and end, but it is not recommended at all, nobody does it and it is considered as a 'bad code'.
Therefore, it is more valid to put them in quotes.