Large-scale effects of ionizing feedback
  I discuss recent work on gas expulsion and triggered star formation in, and
unbinding of, embedded clusters, by ionizing radiation from O-type stars.
Photoionization is not as effective a driver of any of these process as was
perhaps once thought. Although structures such as pillars, bubble and champagne
flows emerge naturally from the action of ionization on turbulent clouds, the
association of stars with such structures does not necessarily imply that they
have been triggered.
