wp-includes/class-wp-rewrite.php:384bool public function using_mod_rewrite_permalinks() { return $this->using_permalinks() && ! $this->using_index_permalinks(); }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.