Evan Birnholz's Guide to the Dec. 27 Post Magazine Crossword

Hi, folks. The Post Magazine puzzle of December 27, "Letter Heads" was an example of a metapuzzle, also known as a meta for short. A meta is a crossword that, in addition to the normal puzzle grid, contains an extra, hidden challenge designed to lead solvers to a unique answer word or phrase. I'm a big fan of this kind of puzzle because I believe that the adrenaline rush one can get from successfully solving a meta is often much greater than the pleasure of finishing a normal crossword. So, fair...