The Rust doc is leaving things out, though whether it’s important is a complicated question. `?` works off off the Try trait (https://doc.rust-lang.org/std/ops

The Rust doc is leaving things out, though whether it’s important is a complicated question. `?` works off off the Try trait (https://doc.rust-lang.org/std/ops/trait.Try.html https://doc.rust-lang.org/std/ops/trait.Try.html), which is unstable so you can’t currently implement it in userland (except on nightly), and it is implemented on more than Option and Result, specifically ControlFlow (https://doc.rust-lang.org/std/ops/enum.ControlFlow.html https://doc.rust-lang.org/std/ops/enum.ControlFlow.html). So whether it’s important to mention depends mostly on how important you think try_fold and try_for_each are, and if you think you’ll miss the information if ever you need those given that’s clearly mentioned in the ControlFlow docs.