If you append_around_filter A.new, B.new, the filter chain looks like

B#before
  A#before
    # run the action
  A#after
B#after

With around filters which yield to the action block, #before and #after are the code before and after the yield.

Source Code

# File action_controller/filters.rb, line 289
def append_around_filter(*filters, &block)
  filters, conditions = extract_conditions(filters, &block)
  filters.map { |f| proxy_before_and_after_filter(f) }.each do |filter|
    append_filter_to_chain([filter, conditions])
  end
end