docs/reference/fidl/language/error-catalog/_fi-0010.md

## fi-0010: Invalid identifier {:#fi-0010}

An identifier was found which does not meet the requirements for valid
identifiers. FIDL identifiers may contain alphanumerics and underscores
(specifically `A-Z`, `a-z`, `0-9`, and `_`), and additionally each identifier
must begin with a letter and end with either a letter or number.

{% 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-0010-a.noformat.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

To fix this, change the identifier to make sure it contains only valid
characters, starts with a letter, and ends with a letter or number.

{% 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-0010-a.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

This error may also occur if a multi-part (dotted) identifier is passed to an
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-0010-b.noformat.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

To fix this, change to use only single-part identifiers in attributes.

{% 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-0010-b.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}
```

Note: This error generally only occurs when an identifier contains all valid
characters, just in an invalid order, such as if an otherwise valid identifier
starts with a number or underscore, ends with an underscore, or if the argument
name for an attribute is a multi-part identifier. If characters which are not
valid in an identifier are used, it will result in some other error, such as
[fi-0001: Invalid Character](#fi-0001).