module Padrino::Helpers::FormHelpers

fields_for :assignment do |assigment| ... end
fields_for @user.assignment do |assignment| ... end
Used within an existing form to allow alternate objects within one form
Constructs form fields for an object using given or default form_builder

def fields_for(object, settings={}, &block)
  builder_class = configured_form_builder_class(settings[:builder])
  fields_html = capture_html(builder_class.new(self, object), &block)
  concat_content fields_html
end