A bag can be used for enclosing something in a container to prevent it from being printed, in normal circumstances. Any mutable list can be used for this purpose, but bags are designed for this purpose. In comparison and sorting, they are declared to be incomparable.
The object Bag is a self initializing type, with ancestor classes MutableList < BasicList < Thing.
The source of this document is in Macaulay2Doc/ov_debugging.m2:771:0.