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Codex

Interested in functions, hooks, classes, or methods? Check out the new WordPress Code Reference!

WPMU Trac

The WPMU Trac was the official bug tracking system for WordPress Multi User until early 2010. It was merged into WordPress Trac during the development of WordPress 3.0 with Multi Site capability, but old MU tickets remain in WPMU Trac as references.

Also see: Debugging WPMU