std::collections provides a complexity for BTreeMap::predecessor but the function is not available

[jbreitbart]

I was just through https://doc.rust-lang.org/std/collections/#maps and noticed that it gives a complexity for the predecessor operation for BTreeMap, but that operation seems not to be available. I checked the map itself and its iterator. Is this a documentation bug or am I missing something?

[LunaBorowska]

This looks a lot like a cursor method, but cursor API for BTreeMap is long gone if it even existed at any point. I think we could write range instead of predecessor here.