wp-includes/pomo/mo.php:35Returns the loaded MO file.
string public function get_filename() { return $this->filename; }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.