Provisional class

The annotation @Provisional('message') marks a feature as provisional.

An API is considered to be provisional if it is still going through the process of stabilizing and is subject to change or removal.

The intent of the @Provisional annotation is to mark APIs that are still in development or that are added only tentatively. Adding the API allows users to experiment with using the APIs, which can provide valuable feedback. Such provisional APIs do not promise stability. They can be changed or removed without warning.

The @Provisional annotation applies to:

• library directives,
• public top-level declarations, and
• public members of public classes.

Provisionality is transitive:

• If a library is provisional, so is every member of it.
• If a class is provisional, so is every member of it.
• If a variable is provisional, so are its implicit getter and setter.

Further, if a class is provisional, so are classes that extend, implement, and mix-in the class.

A tool that processes Dart source code may report when:

• the code imports a provisional library.
• the code exports a provisional library, or any provisional member of  a non-provisional library.
• the code refers statically to a provisional declaration.
• the code dynamically uses a member of an object with a statically known type, where the member is provisional on the static type of the object.

If the provisional use is inside a library, class or method which is itself provisional, the tool should not bother the user about it. A provisional feature is expected to use other provisional features.