Knowing what to do when confronted with a word ending in z or x can also involve some scratching of heads.
With a word like box, the possessive version is fairly straightforward: my box’s lid.
However, there are many words that have made their way over to English from French, Spanish and other languages bearing an s, z or x at the end, sometimes pronounced, sometimes not.
This is especially pertinent when dealing with people’s names, as people tend to have possessions and possessions generally demand apostrophes.
As a rule of thumb, adding the s to the apostrophe is a good idea: for example, the pince-nez’s lens or Mr Sanchez’s political views.
Whereas in the past it was thought bad form to add an s, style guides are now pointing in that direction, even ones in the US where grammar tends to be policed in more traditional ways.
Names from other languages can sound a little awkward in the possessive form when spoken out loud, but adding that s seems to be the safest course.