[xml] xmlRegisterCallbacks usage?

["Grant Goodale" <grant reactivity com>]

        Now that I have 2.5.10 up and running (thanks for the quick
turnaround, Daniel!), I'd like to start using the callbacks
xmlRegisterNodeDefault and xmlDeregisterNodeDefault to observe (and possibly
modify) the DOM tree as it's being built.  Can someone who's familiar with
the code comment on the intended purpose for those callbacks and what their
intended use is?  I have a trivial example working, but looking at the code
I'm not certain how to proceed.

        Thanks in advance,

          Grant
          grant reactivity com