The dom

Hi,
I am working on a research project regarding the DOM. And one of the questions is regarding, What are the issues faced whern developing for a range of platform versions and device vendors.

I ahve searched the Web up and down and its getting really really frustrating because I cannot find an answer.
Can somebody help me please, in maybe directing me in the right direction or if somebody is a DOM Master explain it to me.

Kind regards
Lukas