wp-includes/pomo/mo.php:189string public function export_headers() { $exported = ''; foreach ( $this->headers as $header => $value ) { $exported .= "$header: $value\n"; } return $exported; }Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/pomo/mo.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.