From the foreword:
I love rules. I can’t help it. This document is the culmination of 25+ years of playing one version or another of D&D, though much of the content was written in the last 4 years. I don’t expect anyone to like everything they see here, but it is my hope that every reader finds at least one nugget that they find useful. I can’t help but wonder what this document will look like 25 years from now.
I do want to stress that despite the length of this document, my aim in most cases has been to not overrule the printed rules. The bulk of this document is devoting to expanding them and to clearing up confusion. If you just want to check out the highlights, have a look at the weapon handedness chart, the character with many classes, and the spell errata.