What the?

Well this is the inheritance diagram of the Item Class in the MySQL 5.1 Source tree, nicely documented using the Doxygen tool as mentioned by Jay in his presentation at MySQL Camp.

Jay started the Community Doxygen Project on the Forge to improve the level of commenting enabling a better platform for the community to contribute MySQL server code changes.

At this early stage David Shrewsbury is working on fine tuning initial documentation examples for QA and review. You can check out the Status Page of automated commenting conversion.

You can see the present documentation of MySQL 5.1 source here.