"x" Argument in Optimization.OptimizationProblem

The docs for Optimization.OptimizationProblem refer to u and u₀ but neither are included in the argument list. Should the second positional argument (i.e., x) be relabeled to u? If they’re not representing the same thing, what does x represent?

I know this question is minor but I wanted to make sure I understood the function correctly.

That’s a typo, should be u0.