W3C hosts this yearly five-day event to allow Working Groups (WG) and Interest Groups (IG) to hold their face to face meetings in one place and have the opportunity to meet and liaise with participants from other groups. The W3C Advisory Committee meeting, bi-annual Membership meeting, takes place during the same week.
Unconference/breakout is the preferred format of the Technical Plenary Day. That day will consist of a brief Plenary Session in the morning including a panel on the future of the Internet and Web, with Tim Berners-Lee, Jun Murai, and Vint Cerf that Jeff Jaffe will moderate; and breakout sessions. Please, continue to propose breakout sessions until the Technical Plenary Day itself.