[Dev-luatex] Hooking into the page builder?

Hi All I'd like to use GraphViz to create a graph of the entire node structure of a (simple) page. Keeping the page simple and just for experimentation. Not trying to change any values of node lists, just to output values and structures etc. Before I get too far, is it safe/possible to do this? If so, would anyone have some pseudo code I can use to get me started in the right direction...? Many thanks in advance for suggestions etc. Warm regards Graham