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layout: stdlib-reference
---

# attribute [builtin]

> #### Internal Feature
> The feature described in this page is marked as an internal implementation detail, and is not intended for use by end-users.
> Users are advised to avoid using this declaration directly, as it may be removed or changed in future releases.

## Description

Marks a declaration as a builtin declaration.


## Signature

<pre>
[<a href="builtin.html">builtin</a>]
</pre>