wp-includes/SimplePie/src/Enclosure.php:739Get a single thumbnail
$keyintoptional0string|null public function get_thumbnail($key = 0) { $thumbnails = $this->get_thumbnails(); if (isset($thumbnails[$key])) { return $thumbnails[$key]; } return null; }Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/SimplePie/src/Enclosure.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.