-*- mode: outline; coding: utf-8 -*-

* xml.

** tidy.

  $ tidy -xml -i -utf8 -o out.xml in.xml

or in Emacs C-x h C-x <RET> c utf-8 <RET> C-u M-| tidy -q -xml -i -utf8 -

  http://tidy.sourceforge.net
                home page
  http://www.emacswiki.org/cgi-bin/wiki/tidy.el

** xmllint.

  $ xmllint --format file.xml

or in Emacs: C-x h C-u M-| xmllint --format - <RET>

** Emacs and nxml.

You need introduce line-breaks and then C-x h C-M-\.

** xmlindent.

  http://xmlindent.sourceforge.net/