my website is built in HTML4, and I just realized Freeway gives you the option to export a website in HTML5 or XHTML5. Which HTML should I use? I don’t understand anything about this and have no idea which advantages or cons there are.
Many thanks,

I would go for HTML5, which is the most up-to-date option (along with XHTML5). This also allows you to use HTML5 video and audio elements (rather than outdated QuickTime video/audio) if you need to do that.

You can change this in Document Settings, but if you find that some individual pages remain set on HTML 4, you can change this in the HTML Export panel of the Inspector palette. Check your master page(s) first if this happens, then check your site pages: site pages can override master pages, and master pages can override document settings, but document settings is the place to start.

Thanks, Jeremy! I am going to do it right away.