2 new mishnayot: The openings one cannot make in one's home that is on a courtyard - especially when facing other homes openings, in contrast to facing the public domain. Similarly, one cannot dig under the courtyard or road - unless it's clearly strong enough to support a wagon that is heavily laden with stones. Also, shifting from "building code" to external signs of mourning, in recognition of the building that was destroyed, namely, the Second Temple. Including the proper way of mourning, such that it should be meaningful, but not going so far that the community wouldn't be able to do it.