PRON-POSS
(用以代替his or hers，而不指明是男是女;有人認為這種用法不對)
You use theirs instead of 'his or hers' to indicate that something belongs or relates to a person without saying whether that person is a man or a woman. Some people think this use is incorrect.
例句
He would leave the trailer unlocked. If there was something inside someone wanted, it would be theirs for the taking...
他不會給那個活動房屋上鎖。里面要是有什么別人想要的東西，他們可以盡管拿。
This child is nobody's child until someone makes her theirs officially.
在有人辦理正式手續認領以前，這個孩子不屬于任何人。