Well, we need to avoid the plural for certain.

There would appear, however, to be extra room for the practice of my bugbear (a favourite) regarding the application of "their", all politically correct, when we really do not mean the plural. Under the current verbal regimen, that application will be unavoidable, but I have to (have to, have to, have to, thumping my feet upon the floor, jumping up and down like the well-known dwarf in the grimm tale) animadvert, howl at, vomit up my bile at, the inappropriate and ugly and inelegant (to my mind) appearance of "their" where no plural could be meant.

Let him or her therefore beware of "their", for if "they" practice it, I vow to dance upon "their" grave!!!

cheer

the Ra-ray warrior