  We present a new hybrid Cauchy-characteristic evolution method that is
particularly suited for the study of gravitational collapse in
spherically-symmetric asymptotically (global) Anti-de Sitter (AdS) spacetimes.
The Cauchy evolution allows us to track the scalar field through the different
bounces off the AdS boundary while the characteristic method can bring us very
close to the point of formation of an apparent horizon. Here, we describe all
the details of the method, including the transition between the two evolution
schemes and the details of the numerical implementation for the case of
massless scalar fields. We use this scheme to provide more numerical evidence
for a recent conjecture on the power-law scaling of the apparent horizon mass
resulting from the collapse of subcritical configurations. We also compute the
critical exponents and echoing periods for a number of critical points and
confirm the expectation that their values should be the same as in the
asymptotically-flat case.
