Do HTML5 browsers have to be able to properly process HTML4 tags when the tags appear in HTML5 pages? [closed]

1. Which features are included in HTML5 that were not present in HTML4?
2. Why is HTML5 better than HTML4?
3. Is HTML4 still supported?

Which features are included in HTML5 that were not present in HTML4?

Audio and Video are not part of HTML4 specification. Audio and Videos are integral part of HTML5 specifications e.g. <audio> and<video> tags. It is almost impossible to get true GeoLocation of user browsing any website especially if it comes to mobile devices.

Why is HTML5 better than HTML4?

HTML5 gives developers more control over the performance of their websites. Many of the Flash and JS-based hacks commonly used in HTML4 are now elements inherent to the language. These changes also allow for a faster and smoother user experience.

Is HTML4 still supported?

While all modern browsers technically support HTML4, support for obsolete tags is spotty at best. You should avoid using outdated standards and switch to HTML5.