The ROC constitution says that theyï»¿ are part of China, because they used to be the government of China.  They currently cannot change their constitution under military threat from China.However, legally, neither the ROC nor the PRC has sovereignty over the Formosa (Taiwan) island.The whole China/Taiwan situation is far too complicated to fully discuss here, but it is fascinating, and I encourage anyone interested to take a couple of hours and research the subject.  Make up your own mind.