I'm confused about Gnus's mail-splitting back-ends. How does Gnus decide
which back-end to use?

For example, I have different select methods, including things like
this:

    (setq gnus-select-method '(nnnil "")
          gnus-secondary-select-methods
          '((nnml ""
                  (nnml-directory "~/Mail")
                  (nnml-active-file "~/Mail/active"))
            (nnml "other"
                  (nnml-directory "~/other")
                  (nnml-active-file "~/other/active"))))

Then I have some split rules:

    (setq nnmail-split-methods 'nnmail-split-fancy
          nnmail-split-fancy
          '(|
            ;; Various rules here and the final destination:
            "misc"))

So incoming mail goes normally to "misc" group which is ~/Mail/misc
directory in the file system. But how does Gnus decide to put under
~/Mail and not under ~/other (see my other nnml configuration above)? Is
it possible to put (split) some mail to "nnml:foo" and some to
"nnml+other:bar"?

It seems that none of the examples in Gnus manual tell how to change the
destination back-end or how to split different mail to different
back-ends.

PS. And my terminology may also be wrong. I'm not always sure when to
speak of back-ends, select methods or servers.