Document features deployed behind feature flags

GitLab uses feature flags to strategically roll out the deployment of its own features. The way we document a feature behind a feature flag depends on its state (enabled or disabled). When the state changes, the developer who made the change must update the documentation accordingly.

Every feature introduced to the codebase, even if it's behind a feature flag, must be documented. For context, see the latest merge request that updated this guideline.

When you document feature flags, you must:

Use a note to describe the state of the feature flag

Information about feature flags should be in a Note at the start of the topic (just below the version history).

The note has three parts, and follows this structure:

FLAG:
<Self-managed GitLab availability information.> <GitLab.com availability information.>
<This feature is not ready for production use.>

Self-managed GitLab availability information

If the feature is... Use this text
Available On self-managed GitLab, by default this feature is available. To hide the feature, ask an administrator to [disable the feature flag](<path to>/administration/feature_flags.md) named <flag name>.
Unavailable On self-managed GitLab, by default this feature is not available. To make it available, ask an administrator to [enable the feature flag](<path to>/administration/feature_flags.md) named <flag name>.
Available, per-group On self-managed GitLab, by default this feature is available. To hide the feature per group, ask an administrator to [disable the feature flag](<path to>/administration/feature_flags.md) named <flag name>.
Unavailable, per-group On self-managed GitLab, by default this feature is not available. To make it available per group, ask an administrator to [enable the feature flag](<path to>/administration/feature_flags.md) named <flag name>.
Available, per-project On self-managed GitLab, by default this feature is available. To hide the feature per project or for your entire instance, ask an administrator to [disable the feature flag](<path to>/administration/feature_flags.md) named <flag name>.
Unavailable, per-project On self-managed GitLab, by default this feature is not available. To make it available per project or for your entire instance, ask an administrator to [enable the feature flag](<path to>/administration/feature_flags.md) named <flag name>.
Available, per-user On self-managed GitLab, by default this feature is available. To hide the feature per user, ask an administrator to [disable the feature flag](<path to>/administration/feature_flags.md) named <flag name>.
Unavailable, per-user On self-managed GitLab, by default this feature is not available. To make it available per user, ask an administrator to [enable the feature flag](<path to>/administration/feature_flags.md) named <flag name>.

GitLab.com availability information

If the feature is... Use this text
Available On GitLab.com, this feature is available.
Available to GitLab.com admins only On GitLab.com, this feature is available but can be configured by GitLab.com administrators only.
Unavailable On GitLab.com, this feature is not available.

Optional information

If needed, you can add this sentence:

You should not use this feature for production environments.

Add version history text

When the state of a flag changes (for example, disabled by default to enabled by default), add the change to the version history.

Possible version history entries are:

> - [Introduced](issue-link) in GitLab X.X [with a flag](../../administration/feature_flags.md) named <flag name>. Disabled by default.
> - [Enabled on GitLab.com](issue-link) in GitLab X.X.
> - [Enabled on GitLab.com](issue-link) in GitLab X.X. Available to GitLab.com administrators only.
> - [Enabled on self-managed](issue-link) in GitLab X.X.
> - [Feature flag <flag name> removed](issue-link) in GitLab X.X.
> - [Generally available](issue-link) in GitLab X.X.

Feature flag documentation examples

The following examples show the progression of a feature flag.

> Introduced in GitLab 13.7 [with a flag](../../administration/feature_flags.md) named `forti_token_cloud`. Disabled by default.

FLAG:
On self-managed GitLab, by default this feature is not available. To make it available,
ask an administrator to [enable the featured flag](../administration/feature_flags.md) named `forti_token_cloud`.
The feature is not ready for production use.

When the feature is enabled in production, you can update the version history:

> - Introduced in GitLab 13.7 [with a flag](../../administration/feature_flags.md) named `forti_token_cloud`. Disabled by default.
> - [Enabled on self-managed](https://gitlab.com/issue/etc) GitLab 13.8.

FLAG:
On self-managed GitLab, by default this feature is available. To hide the feature per user,
ask an administrator to [disable the feature flag](../administration/feature_flags.md) named `forti_token_cloud`.

And, when the feature is done and fully available to all users:

> - Introduced in GitLab 13.7 [with a flag](../../administration/feature_flags.md) named `forti_token_cloud`. Disabled by default.
> - [Enabled on self-managed](https://gitlab.com/issue/etc) GitLab 13.8.
> - [Enabled on GitLab.com](https://gitlab.com/issue/etc) in GitLab 13.9.
> - [Feature flag removed](https://gitlab.com/issue/etc) in GitLab 14.0.
> - [Generally available](issue-link) in GitLab 14.0.