-If non-nil, the value should be a string, e.g. \"nnml:\",
-in which case `gnus-group-jump-to-group' offers \"Group: nnml:\"
-in the minibuffer prompt."
+
+If non-nil, the value should be a string or an alist. If it is a string,
+e.g. \"nnml:\", in which case `gnus-group-jump-to-group' offers \"Group:
+nnml:\" in the minibuffer prompt.
+
+If it is an alist, it must consist of \(NUMBER . PROMPT\) pairs, for example:
+\((1 . \"\") (2 . \"nnfolder+archive:\")). The element with number 0 is
+used when no prefix argument is given to `gnus-group-jump-to-group'."