wp-includes/PHPMailer/SMTP.php:1499Get debug output level.
int public function getDebugLevel() { return $this->do_debug; }Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/PHPMailer/SMTP.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.