wp-includes/SimplePie/src/Cache/Memcached.php:140Retrieve the last modified time for the cache
int public function mtime() { $data = $this->cache->get($this->name . '_mtime'); return (int) $data; }Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/SimplePie/src/Cache/Memcached.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.