docs/reference/fidl/language/error-catalog/_fi-0071.md

## fi-0071: Unknown attribute disallowed on strict enum members {:#fi-0071}

A `strict enum` must not have any members annotated with the `@unknown`
attribute:

{% include "docs/reference/fidl/language/error-catalog/label/_bad.md" %}

```fidl
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/bad/fi-0071.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

To continue using the `@unknown` attribute, change to a `flexible enum`:

{% include "docs/reference/fidl/language/error-catalog/label/_good.md" %}

```fidl
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0071-a.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

Otherwise, just remove the attribute altogether to remain a `strict enum`:

{% include "docs/reference/fidl/language/error-catalog/label/_good.md" %}

```fidl
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0071-b.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

The purpose of the `@unknown` [attribute][docs-fidl-attributes-unknown] is to
smooth over a transition from a `strict enum` with a user-defined unknown value,
like this into a `flexible enum` with unknown values known to and handled by
FIDL. In the above example, it would be used to transition from the second
correct usage to the first one.

[docs-fidl-attributes-unknown]: /docs/reference/fidl/language/attributes.md#unknown