module ActiveSupport::Callbacks::ClassMethods

def __update_callbacks(name, filters = [], block = nil) #:nodoc:

:nodoc:
CallbackChain.
This is used internally to append, prepend and skip callbacks to the 
def __update_callbacks(name, filters = [], block = nil) #:nodoc:
  type = CALLBACK_FILTER_TYPES.include?(filters.first) ? filters.shift : :before
  options = filters.last.is_a?(Hash) ? filters.pop : {}
  filters.unshift(block) if block
  ([self] + ActiveSupport::DescendantsTracker.descendants(self)).reverse.each do |target|
    chain = target.send("_#{name}_callbacks")
    yield target, chain.dup, type, filters, options
    target.__reset_runner(name)
  end
end