wp-includes/PHPMailer/PHPMailer.php:4166Validate encodings.
$encodingstringbool protected function validateEncoding($encoding) { return in_array( $encoding, [ self::ENCODING_7BIT, self::ENCODING_QUOTED_PRINTABLE, self::ENCODING_BASE64, self::ENCODING_8BIT, self::ENCODING_BINARY, ], true ); }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.