Having marked some buffers in a buffer menu, how do I execute a
particular command upon them? Specifically, I want to change a
bunch of buffers that are erroneously in "xml-mode" to
"nxml-mode".

This is with 22.2.1.

On Sep 8, 9:06 am, "Sean McLaughlin" wrote:

To apply a function to marked files in dired, use “dired-get-marked-
files”, like this:

;; idiom for processing a list of files in dired's marked files

;; suppose myProcessFile is your function that takes a file path
;; and do some processing on the file

(defun dired-myProcessFile ()
"apply myProcessFile function to marked files in dired."
(interactive)
(require 'dired)
(mapc 'myProcessFile (dired-get-marked-files))
)

I use `ibuffer' as buffer menu. There, pressing E does what you
want. You can try it with M-x ibuffer.