wp-includes/class-wp-rewrite.php:598Retrieves the day permalink structure with month and year.
string|false public function get_day_permastruct() { return $this->get_date_permastruct(); }Introduced in 1.5.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-rewrite.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.