I got about halfway through this before I decided that I just wanted to see the final result. Perusing the source of the final link, I saw a bunch of unclosed tags - is this something that he mentions is allowed in HTML5? I don't think I could bring myself to place unclosed <p> or <td> elements in my page.

As a side note I submitted this post while not logged in, was redirected to the login page, came back to my post and instead of showing "<p>" the input field had rendered a newline. Vulnerability of some sort?