If you want to validate the HTML of a page that is being partially generated in JavaScript, a browser's View Page Source function does not cut it.
To get the page's full HTML content, go into the inspector, right-click on the beginning <html>
tag at the top, and select Copy-> Outer HTML.
Then you can paste this into an HTML file and validate or view it. Just remember to put the <!DOCTYPE html>
tag at the top.