def _keys(result, key_ary, hash)
      hash.each do |key, value|
        key_ary << key
        result << "/#{key_ary.join('/')}"
        _keys(result, key_ary, value) if value.is_a?(Hash)
        key_ary.pop
      end
    end
def _keys(result, key_ary, hash)
      hash.each do |key, value|
        key_ary << key
        result << "/#{key_ary.join('/')}"
        _keys(result, key_ary, value) if value.is_a?(Hash)
        key_ary.pop
      end
    end
Helper for #keys

 @api private