def natural_sort_order(name=nil, &block)
      raise ArgumentError.new("natural_sort_order accepts a method name or a block, but not both") if name && block
      @_natural_sort_order = name || block
    end
def natural_sort_order(name=nil, &block)
      raise ArgumentError.new("natural_sort_order accepts a method name or a block, but not both") if name && block
      @_natural_sort_order = name || block
    end
Define the natural sort order.
 @param [String] name The name of the method that delivers the sort expression
 @param [Block] &block An optional block for complex configurations
 Pass a method name or a block, but not both