  We extend Vaidya's algorithm for the description of a central mass losing or
gaining energy due to electromagnetic-type radiation (`null dust') to the case
of arbitrary radial corpuscular radiation. We also demonstrate the remarkable
possibility of purely algebraic deduction of the Vaidya solution without
integrating the field equations, and interpret this possibility as an artifact
of curvature coordinates. Since Vaidya's approach by itself cannot lead to
certain dependence of mass on spacetime coordinates, the search for a
corresponding mass-function represents an independent issue. In this regard, as
a perspective, we discuss an outlook on the problem of variable masses as a
whole.
