Its and it's

Looking up my old neighborhood of Allston, Mass. (now being colonized by Harvard University), I was surprised to find the following:

Peter Vanderwarker was commissioned by Harvard Planning and the Allston Initiative to photographically capture the spirit of Allston . . . with all it's complexities.

An its/it's error from Harvard--sheesh. You can see it, with a Harvard URL, here.

Its and it's are not that difficult to keep straight. The first is a possessive, like his and hers, neither of which has an apostrophe. It's is a contraction. It's that simple. Or as the writer Jessica Mitford put it,

When is it its? When it's not it is.
When is it it's? When it is it is.

[The offending contraction, from a screenshot. The link to the Harvard page is now dead. “When is it its?” is from Jessica Mitford’s Poison Penmanship: The Gentle Art of Muckraking (1979).]