docs(ref): Set Rust version support expectations

Author: epage

src/doc/src/reference/rust-version.md

@@ -15,8 +15,6 @@ identifiers such as -nightly will be ignored while checking the Rust version.
 
 To find the minimum `rust-version` compatible with your project, you can use third-party tools like [`cargo-msrv`](https://crates.io/crates/cargo-msrv).
 
-When used on packages that get published, we recommend [verifying the `rust-version`](../guide/continuous-integration.md#verifying-rust-version).
-
 > **MSRV:** Respected as of 1.56
 
 ## Uses
@@ -37,3 +35,31 @@ Other tools may also take advantage of it, like `cargo clippy`'s
 [`incompatible_msrv` lint](https://rust-lang.github.io/rust-clippy/stable/index.html#/incompatible_msrv).
 
 > **Note:** The `rust-version` may be ignored using the `--ignore-rust-version` option.
+
+## Support Expectations
+
+These are general expectations; some packages may document when they do not follow these.
+
+**Complete:**
+
+All functionality, including binaries and API, are available on the supported Rust versions under every [feature](features.md).
+
+**Verified:**
+
+A package's functionality is verified on its supported Rust versions, including automated testing.
+See also our
+[Rust version CI guide](../guide/continuous-integration.md#verifying-rust-version).
+
+**Patchable:**
+
+When licenses allow it,
+users can [override their local dependency](overriding-dependencies.md) with a fork of your package.
+In this situation, Cargo may load the entire workspace for the patched dependency which should work on the supported Rust versions, even if other packages in the workspace have different supported Rust versions.
+
+**Dependency Support:**
+
+In support of the above,
+it is expected that each dependency's version-requirement supports at least one version compatible with your `rust-version`.
+However,
+it is **not** expected that the dependency specification excludes versions incompatible with your `rust-version`.
+In fact, supporting both allows you to balance the needs of users that support older Rust versions with those that don't.