[Noisebridge-discuss] Grammar question regarding possessive apostrophe

[Michael Shiloh]

Normally the apostrophe is used to indicate possessive, but I know there 
are many exceptions, such as "its", most of which I don't understand.

Ran across this in an otherwise excellently written document, which made 
me wonder if it's an exception:


	"Strong enough to take a persons weight.

or should it be

	"Strong enough to take a person's weight.

What rule do you follow?

Would this be different in the UK?

Thanks
M