  Choptuik's critical phenomena in general relativity is revisited in the
affine-null metric formulation of Einstein's equations for a massless scalar
field in spherical symmetry. Numerical solutions are obtained by evolution of
initial data using pseudo-spectral methods. The underlying system consists of
differential equations along the outgoing null rays which can be solved in
sequential form. A new two-parameter family of initial data is presented for
which these equations can be integrated analytically. Specific choices of the
initial data parameters correspond to either an asymptotically flat null cone,
a black hole event horizon or the singular interior of a black hole. Our main
focus is on the interior features of a black hole, for which the affine-null
system is especially well adapted. We present both analytic and numerical
results describing the geometric properties of the apparent horizon and final
singularity. Using a re-gridding technique for the affine parameter, numerical
evolution of initially asymptotically flat supercritical data can be continued
inside the event horizon and track the apparent horizon up to the formation of
the final singularity.
