started provisional_features rfc

.gitignore

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+# jetbrains ide stuff
+*.iml
+.idea/
+
+# vscode ide stuff
+*.code-workspace
+.history
+.vscode

rfc/provisional_features.md

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+- Abstract
+
+  Currently, the api for all new features in JupyterLab has to be frozen within the span of a single PR. This is due to the fact that we follow semver; breaking changes may only occur on the occasion of a major version bump.
+
+  This is fine for most features. However, this dev process is causing problems when used for complex features. In particular, features that are expected to be adopted community-wide (eg LabIcon, the extension system, anything to do with user settings) have issues:
+    - These features (including their API) benefit from wide community feedback, and suffer in the vacumn of 1000+ line single PRs
+    - The more complex a feature, the more likely it is for its first draft to have at least some poorly formed or ill-considered API
+
+  To fix this, I propose that we should adopt a formal process for allowing provisional features in the master branch of JuptyerLab core.
+
+- Goals
+  - a better experience for core devs, extension devs, and power users around versioning and compatibility
+  - easier version migration for core and extensions packages
+
+- Terminology
+  - community: JupyterLab core devs, extension devs, and end users
+  - API: public interface, including externally visible package structure, function signatures, CLI, and, in the broadest sense, user interface
+
+- Creating a new provisional feature (Python/Typescript sources)
+  - Create new feature in PR, as per normal
+  - Add a `_PROVISONAL` suffix to all public API
+  - Declare the provisional API in the PR issue thread
+  - Include an outline of future work, including a rough schedule describing the process by which this feature will graduate by the time of the next major release
+
+- Graduating a feature from provisional to mature
+  - A provisional feature may graduate on any minor release
+  - A provisional feature must graduate by the next major release (wrt when it was initally pulled into core) or be removed