attach() is a generic function that allows not only directories and data frames to be attached to the search list, but other classes of object as well. In particular any object of mode list may be attached in the same way:
attach(any.old.list)
It is also possible to attach objects of class pframe, to so-called parametrized data frames, needed for nonlinear regression and elsewhere.
Being a generic function it is also possible to add methods for attaching yet more classes of object should the need arise.