wp-includes/Requests/src/Response/Headers.php:53Set the given item
$offsetstring$valuestring public function offsetSet($offset, $value) { if ($offset === null) { throw new Exception('Object is a dictionary, not a list', 'invalidset'); } if (is_string($offset)) { $offset = strtolower($offset); } if (!isset($this->data[$offset])) { $this->data[$offset] = []; } $this->data[$offset][] = $value; }Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/Requests/src/Response/Headers.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.