Wish list: Two way XSLT

You already knew that you can use an XSLT transformation to convert data from one XML format into another XML format. Something like this:

Last week I remembered that a few years ago, just before I discovered XForms, I was actually looking for an XSLT processor that works bidirectional. Meaning that after the transformation, if you change something in the output document, the equivalent values in the input document also change. Like this:

Back then, there was an alpha quality example project called Wobzilla that demonstrated a technique that works this way. XForms also works this way, but that is a bit less flexible than two way XSLT. The latter can be used in a pipeline and might even function under an XForm to simplify the input/output document used in the XForm.

How difficult is it to create technology like this that works in a Cocoon pipeline or an Orbeon pipeline?

This is a post from 2003 explaining the Wobzilla demonstrator.