docs/reference/fidl/language/error-catalog/_fi-0097.md

## fi-0097: Duplicate union member ordinals {:#fi-0097}

The ordinals used for members in a `union` declaration cannot be repeated:

{% 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-0097.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

Increment the ordinals as needed to ensure that the declaration has unique
ordinals for all of its members:

{% 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-0097-a.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

Alternatively, one of the members with the duplicated name can be removed:

```fidl
{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0097-b.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

The ordinal is used to identify the variant on the wire. If two members share an
ordinal, there is no reliable way to tell which variant is being referred to
when decoding a FIDL message.