  Interacting field theories for systems with a free surface frequently exhibit
distinct universality classes of boundary critical behaviors depending on gross
surface properties. The boundary condition satisfied by the continuum field
theory on some scale may or may not be decisive for the universality class that
applies. In many recent papers on boundary field theories it is taken for
granted that Dirichlet or Neumann boundary conditions decide whether the
ordinary or special boundary universality class is observed. While true in a
certain sense for the Dirichlet boundary condition, this is not the case for
the Neumann boundary condition. Building on results that have been worked out
in the 1980s, but have not always been appropriately appreciated in the
literature, the subtle role of boundary conditions and their scale dependence
is elucidated and the question of whether or not they determine the observed
boundary universality class is discussed.
