Add more detailed versioning policy (#197)

CONTRIBUTING.md

@@ -23,11 +23,14 @@ CPython's `main` branch.
 # Versioning scheme
 
 Starting with version 4.0.0, `typing_extensions` uses
-[Semantic Versioning](https://semver.org/). The major version is incremented for all
-backwards-incompatible changes.
+[Semantic Versioning](https://semver.org/). See the documentation
+for more detail.
 
 # Workflow for PyPI releases
 
+- Make sure you follow the versioning policy in the documentation
+  (e.g., release candidates before any feature release)
+
 - Ensure that GitHub Actions reports no errors.
 
 - Update the version number in `typing_extensions/pyproject.toml` and in

doc/index.rst

@@ -37,6 +37,17 @@ In view of the wide usage of ``typing_extensions`` across the ecosystem,
 we are highly hesitant to break backwards compatibility, and we do not
 expect to increase the major version number in the foreseeable future.
 
+Feature releases, with version numbers of the form 4.N.0, are made at
+irregular intervals when enough new features accumulate. Before a
+feature release, at least one release candidate (with a version number
+of the form 4.N.0rc1) should be released to give downstream users time
+to test. After at least a week of testing, the new feature version
+may then be released. If necessary, additional release candidates can
+be added.
+
+Bugfix releases, with version numbers of the form 4.N.1 or higher,
+may be made if bugs are discovered after a feature release.
+
 Before version 4.0.0, the versioning scheme loosely followed the Python
 version from which features were backported; for example,
 ``typing_extensions`` 3.10.0.0 was meant to reflect ``typing`` as of