From the introduction:
Welcome to Expeditious Retreat Press’ newest free product, A Magical Society: Guide to Monster Statistics. This 19 page PDF breaks down the D20 monster stat block, delineating the interconnectivity between statistics, how each entry shapes a monster’s CR, and how to properly present information within the monster stat block.
Besides being an excellent resource in and of itself, A Magical Society: Guide to Monster Statistics is an entire chapter from a larger work, A Magical Society: Beast Builder. A Magical Society: Beast Builder weighs in at a whopping 256 pages, covering the following concepts: what makes a good monster, how monsters fit in their environment, classifying monsters by their function rather than their physiology, breaking down types and subtypes, demystifying templates, how to use bits and pieces from monsters to enrich your game, and a comprehensive list of 600 special attacks and special qualities taken from the SRD and Monster Geographica: Underground.