If set to a ring, then when calling divisor, the primes are all checked whether they are ideals in that ring.
The object AmbientRing is a symbol.
The source of this document is in /build/macaulay2-88fgJW/macaulay2-1.25.11+ds/M2/Macaulay2/packages/WeilDivisors.m2:2038:0.