We propose an axiomatic ontological framework for informational templates based on former works on slot-mereology. Templates and their parts can be filled by information content entities, but can exist even if unfilled. Thus, we represent templates as slots that can themselves have slots, where the "slot of" relation between slots can be interpreted as a parthood relation. Some slots of a slot are mandatory and need to be filled for the parent slot to be filled, whereas others are optional and do not have this restriction. The structure of a filler is also described by slots of a different nature. We discuss how parthood between slots can be connected with parthood between their fillers.