When this strategy is used then the degree of the map is computed directly from the multiplicity of $[H_m^1(Rees(I))]_0$. It contains an implementation of Corollary 2.12 in Degree and birationality of multi-graded rational maps.
The object Hm1Rees0Strategy is a symbol.
The source of this document is in /build/reproducible-path/macaulay2-1.25.05+ds/M2/Macaulay2/packages/MultiGradedRationalMap.m2:1145:0.