Departing from nanjing to Taiwan and then returning to Frankfurt via Hong Kong

Hi,

I will be travelling to Nanjing from Farnkfurt, but I want to travel to Taiwan and return to Frankfurt via Nanjing. Do I have to get a multiple entry visa or am I eligible for this transit option? Also I don't understand what you mean when you say Hong Kong, Macau and Taiwan are regarded as a third region in terms of transit issues. Does that mean that any travel to them is treated the same as travelling to any other part of China?