When I rewrote the Presentation Engine from scratch, it never even occurred to me validate it using the w3 validation tools available online. Then while chatting on a forum today, the thought suddenly occurred to me. So I initially ran the site through the validator (just the front page) and received 178 markup errors. A quick look over the errors revealed that some quick changes to the source would resolve 95% of the errors without too much effort.
So after doing that, I sat down and hammered out the last 5%, none of which were too difficult. Suddenly I find that I have a standards compliant CSS based layout website that renders across all three major browsers with no issues. Today is definitely a good day as this is a nice milestone to have reached. I even found the motivation to re implement the "Quote of the Day" functionality that was present in older versions of the Presentation Engine (see below the logo on the front page). This means that the first beta release of version 3.5 should occur soon now that the code base has reached a feature complete stage. I simply need to build a valid demo database and throw together a couple sample themes that I will provide with the download.