For debate watchers, this MAY help you understand what you're seeing tonight. Mark Halperin at Time magazine has obtained the official 2012 presidential debate rules and put them on his blog. This is the agreement reached by the two campaigns and neither the Commission on Presidential Debates nor the moderators were parties to it. Highlights below, see it all here.
What would happen if another candidate qualified for the debates.
The candidates agreed not to publicly call for any additional debates beyond the Commission-sponsored events.
Candidates aren’t allowed to cite anyone in the audience (besides family members) during the debate.
Candidates aren’t allowed to address questions to each other or ask the other candidate to take a pledge.
The moderators can’t do “show of hands” questions.