From IdefixWiki

XML

Installing the plugin

see http://www.xmlhack.com/read.php?item=2061

Download the plugin nxml-mode-20041004.tar.gz from:
http://www.thaiopensource.com/download/

Unpack it to ~./xemacs/nxml/

Edit ~./xemacs/init.el:

;; add xml to load-path
(setq load-path (cons (concat (aw-make-package-path "nxml") my-dir-sep) load-path))

;; XML
(load "rng-auto.el")
(setq auto-mode-alist
      (cons '("\\.\\(xml\\|xsl\\|rng\\|xhtml\\)\\'" . nxml-mode)
	    auto-mode-alist))
 

Realtime checks in Emacs

At first we need to convert the xml-schema file into a rnc file. For this download the program trang-20030619.zip from:
http://www.thaiopensource.com/download/

Execute it with:

java -jar trang.jar -I xml -O rnc ui.xsd test.rnc

Now you can load the file test.rnc with emacs from the menu XML->Set Schema->File...