The site is known as "mdn web docs", and the URL is developer.mozilla.org
Progressive Enhancement is the idea of maintaining a baseline of accessibility to everyone, while continuing to be updated to the most recent versions of browsers.
Progressive enhancements are needed to make sure the website can be navigated by anyone regardless of any impairment they might have. This may involve having a screen reader reading out the webpage, and including alternate text for images and other graphics that appear on the page.
No, the home page does not validate.
No, the second page does not vaildate either.
The first page has 37 validation errors, while the second page has 35 errors.
The website gets an overall 9/10 regarding design. It's clean, there's no extra graphics or padding to get to the information, and its all readily available.
The site gets a 10/10 for usability, as it has has everything someone browsing the site would need. There's also several links to other articles within the article regarding progressive enhancement, so users can learn more about what specific things mean.
Yes, the site does meet its purpose by providing information regarding progessive enhancements.