wp-includes/PHPMailer/PHPMailer.php:3854Encode a string in quoted-printable format.
$stringstringstring public function encodeQP($string) { return static::normalizeBreaks(quoted_printable_encode($string)); }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.