is f.submit in a form_for newer than submit_tag?

some books or even the rails api uses

form_for ...
  ...
  submit_tag ...
end

and i found that the Rails 2.3.2 Scaffold uses

f.submit "Go"

instead... and this is not in the rails api doc. Is this a new
addition and is it suppose to replace submit_tag?

All the method in the form helper have his "object implicit"
counterpart, for example you can call text_field(object_name, method,
options = {}) or f.text_field(method, options = {}) and the object
used is f.object (the parameter of form_for @something), they produce
exactly the same output.

Regards.

Franco Catena.