  We revisit H. Foellmer's concept of quadratic variation of a cadlag function
along a sequence of time partitions and discuss its relation with the Skorokhod
topology. We show that in order to obtain a robust notion of pathwise quadratic
variation applicable to sample paths of cadlag processes, one must reformulate
the definition of pathwise quadratic variation as a limit in Skorokhod topology
of discrete approximations along the partition. One then obtains a simpler
definition of quadratic variation which implies the Lebesgue decomposition as a
result, rather than requiring it as an extra condition.
