;;;###autoload
(defun vc-root-diff (historic &optional not-urgent)
- "Display diffs between file revisions.
-Normally this compares the currently selected fileset with their
-working revisions. With a prefix argument HISTORIC, it reads two revision
+ "Display diffs between VC-controlled whole tree revisions.
+Normally, this compares the tree corresponding to the current
+fileset with the working revision.
+With a prefix argument HISTORIC, prompt for two revision
designators specifying which revisions to compare.
The optional argument NOT-URGENT non-nil means it is ok to say no to