A Hasse graph is a Hasse diagram ready for display. It contains labels instead of Weyl group elements and reflections.
The object HasseGraph is a type, with ancestor classes BasicList < Thing.
The source of this document is in /__w/M2/M2/macaulay2-1.26.05+ds/M2/Macaulay2/packages/WeylGroups.m2:4374:0.