Feature development happens as follows:
A MySQL feature is specified in a Worklog entry.
The Worklog entry undergoes specification, design, architecture and QA reviews (but not necessarily in a strict sequence).
The MySQL feature is implemented in a feature tree.
Feature trees are created from and kept in sync with the MySQL main development tree, which is called TRUNK.
When a feature has been implemented, it undergoes a code review.
When the code review is done, the feature tree is handed over to QA (quality assurance).
QA tests the feature, the implementer fixes bugs, and QA eventually "signs off" the feature.
Once the feature is signed off, it is merged into TRUNK.
This way, TRUNK will accumulate features and bug fixes over time. Extensive regression testing is performed on TRUNK all the time, keeping TRUNK close to Release Candidate (RC) quality at all times.