Is HK-Macau-Taiwan considered one region?

Good question. Actually, Hong Kong, Taiwan and Macau, although not a countries are considered as the third countries for the purpose of obtaining 144 hours visa free transit. This is perfectly according to the Chinese TWOV rules. To conclude, you can really use these three territories to travel to and from mainland China and enjoy 144 hours visa free transit and each of them is considered to be a separate territory. For example, you can take a flight from Macau to Beijing, stay there for 144 hours visa free and then take a plane to Taiwan. After that, you can take a plane from Taiwan to Shanghai and then travel to Hong Kong... Basically, you just have to be a bit creative, find affordable flights and use the mentioned territories to visit several parts of mainland China and in reality never going to far from the mainland area.

Thanks for the clarification, much appreciated!