The type of all method functions created with the option Binary set to true, such as gcd.
The object MethodFunctionBinary is a type, with ancestor classes FunctionClosure < Function < Thing.
The source of this document is in /__w/M2/M2/macaulay2-1.26.05+ds/M2/Macaulay2/packages/Macaulay2Doc/ov_methods.m2:570:0.