html5shiv - why is it only for IE?

Question

I want to start using some HTML5 tags, but worried how it will render on browsers that do not support HTML5. It seems like html5shiv is a solution I can use for IE browsers <

Answer 1

First, to be clear, html5shiv just makes it so that you can style certain HTML5 tags (section, article, etc.) correctly. It does not give the browser "HTML5 support" in any more general sense of the term.

With that in mind, note that IE <9 are the only browsers that don't allow styling of these HTML5 tags correctly, so that's why html5shiv only applies to them.

Other browsers (even very old ones like Netscape Communicator 4) will still parse the unrecognized tags correctly and allow CSS to apply to them as you would expect.

As zzzzBov notes in his answer, they might not have the correct default styles (which in most (all?) cases are either display: block or nothing), so you'd need to add those even for non-oldIE browsers. But doing so works fine in non-oldIE browsers, whereas in oldIE, adding these default styles---or any styles whatsoever---only works if you use html5shiv.