xmlformat is a REX-based script (take your pick from Perl or Ruby versions) for consistently reformatting XML files; that is, "canonizing" and normalizing whitespace, indenting, line-wrapping, and placement of line breaks. It works as advertised, handling mixed content and "verbatim" content correctly.

xmlformat (developed by MySQL guru Paul DuBois[1]) is a tool to use when you want an off-the-shelf solution for "pretty printing" XML files for better readability--or, more importantly, when you want to ensure that before being committed to a revision-control system and/or having diffs run against your files, the whitespace, indenting, line-wrapping, and placement of line breaks in them have been put into a standard, consistent format.

A tool like xmlformat is especially useful in environments where you have multiple people working on the same set of XML files--people who may be using a variety of editing applications to edit the files. As DuBois puts in his intro to the xmlformat documentation:

The good news about xmlformat specifically (as opposed to some other XML "pretty printing" tools) is that it actually always seems to do what you'd expect it to do; after doing some initial configuration to teach it about your content--for example, to tell it which elements in your XML files are inline elements and which are block elements, which need to be handled as "verbatim" elements, and which you want it to whitespace-normalize--I think you'll find that it reformats your content the way you want it, without unexpectedly removing or introducing any whitespace (including handling mixed content correctly).[2]

Clear, well-written documentation on how to configure xmlformat is provided both in the xmlformat distribution and online. The documentation also includes details about how it works[3]. The xmlformat Perl and Ruby scripts themselves are also extensively commented and make for an interesting read.