wp-includes/rest-api/class-wp-rest-request.php:997Sets a parameter on the request.
$offsetstring$valuemixed #[ReturnTypeWillChange] public function offsetSet( $offset, $value ) { $this->set_param( $offset, $value ); }Introduced in 4.4.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/rest-api/class-wp-rest-request.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.