If $G$ is a Grassmannian (i.e. a FlagBundle with rank sequence of length 2), and if the Schubert ring of $G$ has already been built, then it is stored in G.cache.SchubertRing. This should not be used as an accessor; see schubertRing.
The object SchubertRing is a symbol.
The source of this document is in /build/reproducible-path/macaulay2-1.25.06+ds/M2/Macaulay2/packages/Schubert2.m2:1857:0.