# File lib/action_view/helpers/form_helper.rb, line 605 def fields_for(record_name, record_object = nil, options = {}, &block) builder = instantiate_builder(record_name, record_object, options, &block) output = capture(builder, &block) output.concat builder.hidden_field(:id) if output && options[:hidden_field_id] && !builder.emitted_hidden_id? output end