docs/reference/fidl/language/error-catalog/_fi-0004.md

## fi-0004: Invalid hex digit {:#fi-0004}

Unicode escapes in string literals must not contain invalid hex digits:

{% 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-0004.noformat.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

You must specify a valid [Unicode code point] in hexadecimal, from 0 to 10FFFF.
Each hex digit must be a number from 0 to 9, a lowercase letter from `a` to `f`,
or an uppercase letter from `A` to `F`. In this case, `G` was a typo for `F`:

{% 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-0004.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

[Unicode code point]: https://en.wikipedia.org/wiki/Unicode#Codespace_and_Code_Points