The PSPad text editor integrates Tidy to format Html document. It has a few Tidy configurations, for wrapping html documents, cleaning document, converting documents to use css, etc. But you can also use Tidy to format your Xml documents. Add the following Tidy configuration:

[TiDy format XML]
add-xml-decl:yes
add-xml-pi:yes
alt-text:Image
break-before-br:no
doctype:AUTO
drop-empty-paras:no
drop-font-tags:yes
fix-bad-comments:yes
hide-endtags:no
char-encoding:raw
indent:yes
indent-spaces:2
input-xml:yes
output-xml:yes
quiet:yes
tidy-mark:no
uppercase-attributes:no
uppercase-tags:no
word-2000:no
wrap:100
wrap-asp:yes
wrap-attributes:yes
wrap-jste:yes
wrap-php:yes
write-back:yes