Applying log on a generating function

Question

I am reading the Book SymmetricFunctions and Hall Polynomials by MacDonald and now reached the chapter "Power Sums" (Starting on Page 23). There we want to proof $[P(t)=H'(t)/H(t)]$ In the last step of the proof we get

$P(t) = \frac{\partial}{\partial t}log(H(t)),$ where $H(t)$ is a generating function.
What does $log$ of a generating function mean??? Is this the same as applying $log$ on a "normal" power series?