  Scalar field dark energy evolving from a long radiation- or matter-dominated
epoch has characteristic dynamics. While slow-roll approximations are invalid,
a well defined field expansion captures the key aspects of the dark energy
evolution during much of the matter-dominated epoch. Since this behavior is
determined, it is not faithfully represented if priors for dynamical quantities
are chosen at random. We demonstrate these features for both thawing and
freezing fields, and for some modified gravity models, and unify several
special cases in the literature.
