What Is the Didache?

In the recent exchange that I posted on the blog (dealing with the existence of Q) the document known as the Didache was mentioned – especially by guest contributor Alan Garrow, who thinks that the Didache was a source used by the authors of Matthew and Luke.  I think even Alan will agree that this is a highly anomalous view; I don’t know of any other scholar who accepts it (though if Alan knows of any who do, I’m sure he can tell us in a comment).  The Didache is almost always assumed to hav...