The site's name is W3Schools. Its purpose is to teach people how to code.
The site's home page does validate.
The second page validates.
Nine errors/warnings may exist on the home page. Twenty-three errors/warnings may exist on the second page.
I would rate the site's design a 10. Everything is organized and spaced out nicely.
I would rate the site's usability a 10. Everything you want to know can be easily found.
The site does meet its purpose.