I am reading this note on super-Riemann surfaces. In the second paragraph of section 7.4.1 (page 87), there is a statement that I am trying to understand:
The compactified moduli space of closed oriented Riemann surfaces has no boundary.
However, as it is mentioned, the compactified moduli space of surfaces with boundary is an orbifold with boundary.
Can someone please elaborate these points and that why the compactified moduli space of closed oriented Riemann surfaces does not have boundaries and is just compact? A good pedagogical reference on the Deligne-Mumford compactification is highly appreciated.