Policy: Past behavior

I'd like the authoring guide to have guidance on whether or not to include information about past versions of Rust. If we do allow it, what is the guidance for how to do that?

I would prefer to generally avoid references to older versions, but I acknowledge that there are some rare cases where it is truly helpful. Is there some nuance or balance for that?

https://github.com/rust-lang/spec/issues/34#issuecomment-1973739688 mentions that rfc3355 says:

The specification is specific to the latest version of Rust. [...]

While the specification might include notes about the Rust version that a feature was introduced in for informative purposes (similar to standard library documentation), it does not attempt to accurately specify older, unsupported versions of Rust.

The Vision blog post says:

The descriptive definitions tell the reader how a construct will behave with
respect to a specific Rust version (e.g. Rust 1.76).

Start by reading RFC 3355 and the linked Rust Reference specification discussion, then compare them with the Rust specification vision post. The work is done when the authoring guide contains agreed guidance on whether and how to discuss past Rust versions, including the permitted nuance for rare cases.