Quite a lot, actually. Most of the modern HTML5 is geared towards web and mobile apps, really. You can build most sites with old HTML4. Unless peeps are using a

Quite a lot, actually. Most of the modern HTML5 is geared towards web and mobile apps, really. You can build most sites with old HTML4. Unless peeps are using a big-name CMS, most sites are still running on old HTML standards.