wp-includes/class-wp-query.php:4668Determines whether the query is for a sitemap.
bool public function is_sitemap(): bool { return $this->is_sitemap; }Introduced in 7.1.0.
Signature, return type and hooks compared across 1 parsed release.
src/wp-includes/class-wp-query.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.