What does NSExpression *lhs, and NSExpression *rhs mean?

I know what an NSExpression is, but all over the place I see these cryptographic variable names like lhs and rhs.

Yes, I can guess 开发者_如何学Pythonit means something leftFoo and rightFoo, but what does "hs" stand for? No idea.

"Left-hand side" and "right-hand side". The left-hand side is on the left of the comparison operator, and the right-hand side is on the right.

"left-hand side" and "right-hand side" (of the expression's operator).

This abbreviation is seldom if ever used in print; it is very informal. (source)

Apparently API docs are very informal, too :)