Extend doc:app rake task to Include lib/*?


I’ve never really done much with rake and I’m trying to figure out how
to add some options to the doc:app task. For instance I’d like to
include documentation for files in the lib directory. I can’t seem to
figure out the proper way to do it short of changing the
lib/tasks/documentation.rake in the rails distribution. After poking
around in the rails tasks, I tried creating an extended_docapp.rake in
my lib/tasks that contains this:

namespace :doc do
task :app do |rdoc|

But when I run rake doc:app I get this error:

rake aborted!
undefined method `rdoc_files’ for #Rake::Task:0x2299c00

I guess I’m not referencing the task correctly? I don’t want to
overwrite the task, just want to add that option. I can’t seem to
find any documentation on extending the built in rails tasks. Is it
possible to do what I’m trying to do and whats the proper way?