Multi parameter attributes?

Have a look at the source code of
ActiveRecord::Base#assign_multiparameter_attributes and following.

Basically, if you have a class-typed attribute (i.e
not :string, :integer and so on) where the constructor of the class
takes multiple arguments, you can indicate position and type of these
arguments in parentheses. In this way something(1i), something(2s),
something(3f) are mapped to

So, if you want to use this in a helper method, you just have to make
sure that it generates suitably named form elements

  <input type="text" name="something(1i)" />
  <input type="text" name="something(2s)" />
  <input type="text" name="something(3f)" />