The headline feature of WordPress 2.3 was what Matt called “native tagging support”. The taxonomy architecture that supported tags in WP 2.3 – an abstraction of the old Category functionality – is a critical component of how WordPress turned from a blogging platform to the more generalized content management system that it is today.

But this evolution has not always been smooth sailing. There was significant debate over how (and whether) WordPress’s general taxonomy framework should work. And the database schema that ultimately shipped in version 2.3 had technical ramifications that took several years to become fully apparent.

A close look at these problems, and how the WordPress team is addressing them, contains some useful lessons on how WP deals with breaking changes, the importance of unit tests and developer documentation, and how to weigh backward compatibility against future platform growth.