This part represents a combination taken from some set of subjects. It uses the binary expansion of its RID as a bitmask, with each bit representing the presence of a corresponding subject in the combination. The rootSubjects component is used to generate an array of nodes corresponding to each root subject. If the getChildSubjects action is provided, it is used to expand these root nodes into a forest with the final list of maskable nodes being populated by a depth-first search over the root subjects. If the getChildSubjects action is not provided, the final array of nodes will be a flat array corresponding to the root subjects.