So if an older browser doesn't support them, the fact that they're in the HTML won't 'break' anything, they’ll just be rendered as an NB While client-side form validation is great for enhancing user experience—fast, instant feedback to the user without making a round trip to the server—you will still need to validate any data submitted on the server, too.
Let's walk through an example of how we can validate a form using only the browser's built in validation.
In tandem with the new input types and attributes provided by HTML5, CSS3 gives us some new pseudo-classes we can use to provide visual clues to the user as to which form fields are required, which are optional, and which contain validation errors.
But the great thing about them is that they all degrade gracefully.
After making all these changes our HTML now looks like this: https://jsfiddle.net/ianoxley/9C2JD/ The good news is that HTML form validation is supported by all the latest desktop browsers, and most mobile browsers.
The bad news is that it is only partially supported in Safari, and isn't supported at all on i OS Safari, or the default Android browser.
If you still haven’t heard, hear it now: FRAMES ARE DEAD – well, technically, they are more like the undead – the zombies of webdesign.
They should be gone and forgotten but refuse to stay buried. However, there may be a situation, where inserting a separate html document into your page makes sense.