Title: HeadersCollection::set
Published: May 20, 2026

---

# HeadersCollection::set( string $name, string|WordPressAiClientProvidersHttpCollectionslist $value ): void

## In this article

 * [Parameters](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/set/?output_format=md#parameters)
 * [Return](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/set/?output_format=md#return)
 * [Source](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/set/?output_format=md#source)
 * [Related](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/set/?output_format=md#related)
 * [Changelog](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/set/?output_format=md#changelog)

[ Back to top](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/set/?output_format=md#wp--skip-link--target)

This function’s access is marked private. This means it is not intended for use 
by plugin or theme developers, only by core. It is listed here for completeness.

Sets a header value, replacing any existing value.

## 󠀁[Parameters](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/set/?output_format=md#parameters)󠁿

 `$name`stringrequired

The header name.

`$value`string|<span class="WordPressAiClientProvidersHttpCollectionslist”>WordPressAiClientProvidersHttpCollectionslistrequired

The header value(s).

## 󠀁[Return](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/set/?output_format=md#return)󠁿

 void

## 󠀁[Source](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/set/?output_format=md#source)󠁿

    ```php
    private function set(string $name, $value): void
    {
        if (is_array($value)) {
            $normalizedValues = array_values($value);
        } else {
            // Split comma-separated string into array
            $normalizedValues = array_map('trim', explode(',', $value));
        }
        $lowerName = strtolower($name);
        // If header exists with different casing, remove the old casing
        if (isset($this->headersMap[$lowerName])) {
            $oldName = $this->headersMap[$lowerName];
            if ($oldName !== $name) {
                unset($this->headers[$oldName]);
            }
        }
        // Always use the new casing
        $this->headers[$name] = $normalizedValues;
        $this->headersMap[$lowerName] = $name;
    }
    ```

[View all references](https://developer.wordpress.org/reference/files/wp-includes/php-ai-client/src/providers/http/collections/headerscollection.php/)
[View on Trac](https://core.trac.wordpress.org/browser/tags/7.0/src/wp-includes/php-ai-client/src/Providers/Http/Collections/HeadersCollection.php#L99)
[View on GitHub](https://github.com/WordPress/wordpress-develop/blob/7.0/src/wp-includes/php-ai-client/src/Providers/Http/Collections/HeadersCollection.php#L99-L118)

## 󠀁[Related](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/set/?output_format=md#related)󠁿

| Used by | Description | 
| [HeadersCollection::__construct()](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/__construct/)`wp-includes/php-ai-client/src/Providers/Http/Collections/HeadersCollection.php` |

Constructor.

  |

## 󠀁[Changelog](https://developer.wordpress.org/reference/classes/wordpress-aiclient-providers-http-collections-headerscollection/set/?output_format=md#changelog)󠁿

| Version | Description | 
| [0.1.0](https://developer.wordpress.org/reference/since/0.1.0/) | Introduced. |

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