# File lib/active_support/vendor/i18n-0.4.1/i18n/backend/flatten.rb, line 54
      def flatten_keys(hash, escape, prev_key=nil, &block)
        hash.each_pair do |key, value|
          key = escape_default_separator(key) if escape
          curr_key = [prev_key, key].compact.join(FLATTEN_SEPARATOR).to_sym
          yield curr_key, value
          flatten_keys(value, escape, curr_key, &block) if value.is_a?(Hash)
        end
      end