What is the folder tree vendor/rails/... for?

Hi all,

I have been trying to work out why a set of functional tests have been
failing in a RoR book project I have been following (in Patrick Lenz’s
book BYORORWA). I have discovered that in the sample application there
is a set of folders starting with vendor/rails/… This set of folders
is not created when I create a new project using “rails [nameofproject]”
and it is not in any of my old RoR projects either. However, if I put
that folder tree in my application the functional tests all pass. Also,
removing the tree from the sample application causes it to fail with the
exact same failures and errors that I had in my version of the
application. So it seems pretty certain that the absence of these
folders makes the functional tests fails.

Can anyone tell me whether my Rails installation should be creating this
folder tree in my own projects, and it would be great to know what the
folder tree actually does.

Thanks,