options_with_prefix

# File actionpack/lib/action_view/helpers/date_helper.rb, line 665
        def options_with_prefix(position, options)
          prefix = "#{@object_name}"
          if options[:index]
            prefix << "[#{options[:index]}]"
          elsif @auto_index
            prefix << "[#{@auto_index}]"
          end
          options.merge(:prefix => "#{prefix}[#{@method_name}(#{position}i)]")
        end