Rails - Aug 2006 - undefined method ''render_component_as_string'' - why?

I want to put a ''search_box'' text_field in the header of each
page.
The search_box is implemented in a controller named ''users''.
(so Controller_A is calling a component in Controller_B)

When I add this line to my ''controllers/application.rb'' file,
I don''t
understand why I get and ''undefined method'' error.  After all,
"class
ApplicationController < ActionController::Base".

@sbox = render_component_as_string(:controller=>''users'',
:action=>:search)

My problem is very similar to the the one described in a post to this list 6
months ago:
http://lists.rubyonrails.org/pipermail/rails/2006-February/016759.html

Nobody ever explained it then.  I corresponded with the February poster, who
points out that it is ''protected'', and suggests that is why
Controller_A
can''t call an Action in Controller_B. But some folks on the Site5
forums, as
well as the book authors (Dave Thomas, ''Agile Web Development with
Rails'',
Chad Fowler, ''Rails Recipes'') claim to make cross-controller
calls.  And if
cross-controller invocations simply didn''t work, the whole point of
Components would be greatly diminished.

I also read this nice ''components'' doc
http://manuals.rubyonrails.com/read/chapter/71
...
which leaves a little unclear if both ''render_component'' and
''render_component_as_string'' can both be called from either a
View or
Controller, but I think the doc is saying that either method can be called
from either location.  So why is it ''undefined''?
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
http://wrath.rubyonrails.org/pipermail/rails/attachments/20060814/13911981/attachment.html