A few more thoughts for consideration:

* We already have a toprettyxml() tool in the minidom package.

* Since whitespace is significant in XML, prettifying changes the content and meaning, so it doesn't round-trip and should only be used for debugging purposes.

* Usually, I recommend using XML viewers such as the one built into the Chrome browser.  That provides indentation without changing meaning. It also lets you run searches and conveniently supports folding and unfolding elements.   I would rather someone use a viewer rather than something like toprettyxml().