The grab-bag of policies regarding which agency functions and in some cases which entire agencies remain open reflects the variation in how government work is funded. The TSP governing agency, for example, is self-funded from fees charged against investor accounts and is open for business; similarly, the Postal Service does not draw regular appropriations but gets its operating money from the services it provides. Within certain agencies that do draw appropriations, certain functions are self-funding, for example functions that administer trust funds and get their operating money from them. In addition, certain agencies are allowed to use certain fees they collect—the federal courts, for example, apparently would be able to remain open several weeks using such funding—some programs operate under multi-year funding, and there are other variants.
