I was really surprised when I finally figured out that all I had to do was: (on my Debian system) aptitude install w3c-markup-validator and opening http://l

I was really surprised when I finally figured out that all I had to do was: (on my Debian system) aptitude install w3c-markup-validator and opening http://localhost/w3c-validator/ http://localhost/w3c-validator/ in the browser. Unfortunately, HTML5 is not supported out of the box. However, this might be added as described in: http://blog.simplytestable.com/installing-the-w3c-html-validator-with-html5-support-on-ubuntu/ http://blog.simplytestable.com/installing-the-w3c-html-valid...