wp-includes/PHPMailer/PHPMailer.php:3354Format a header line.
$namestring$valuestring|intstring public function headerLine($name, $value) { return $name . ': ' . $value . static::$LE; }Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/PHPMailer/PHPMailer.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.