Implement DTD (or, in general, schema) based indentation/pretty-printing

Since Woodstox-3.0 will have flexible, pluggable writer-side validation framework (and support at least DTD, initially), it will be possible to implement indentation ("pretty-printing") quite easily.
Although from inter-operability perspective indentation is irrelevant, it's nice to be able to produce something that is more pleasing to human eye, for debugging; especially something that can be turned on during development and then disabled in production.

So, it'd be great if this could be implemented for Woodstox-3.0. And if not, definitely for 4.0.