def callback(event, buffer = nil, start = nil, the_end = nil)
      return if !start.nil? && start == the_end
      if @callbacks.has_key? event
        @callbacks[event].call(buffer, start, the_end)
      end
    end
def callback(event, buffer = nil, start = nil, the_end = nil)
      return if !start.nil? && start == the_end
      if @callbacks.has_key? event
        @callbacks[event].call(buffer, start, the_end)
      end
    end
Issues a callback.